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Bureau of Mines Information Circular/ 1983 



In Situ Copper Leaching 

in the United States: 

Case Histories of Operations 

By Jon K. Ahlness and Michael G. Pojar 




UNITED STATES DEPARTMENT OF THE INTERIOR 



Information Circular 8961 



In Situ Copper Leaching 

in the United States: 

Case Histories of Operations 

By Jon K. Ahlness and Michael G. Pojar 




UNITED STATES DEPARTMENT OF THE INTERIOR 

William P. Clark, Secretary 

BUREAU OF MINES 
Robert C. Horton, Director 




.\AV* 



As the Nation's principal conservation agency, the Department of the Interior 
has responsibility for most of our nationally owned public lands and natural 
resources. This includes fostering the wisest use of our land and water re- 
sources, protecting our fish and wildlife, preserving the environmental and 
cultural values of our national parks and historical places, and providing for 
the enjoyment of life through outdoor recreation. The Department assesses 
our energy and mineral resources and works to assure that their development is 
in the best interests of all our people. The Department also has a major re- 
sponsibility for American Indian reservation communities and for people who 
live in Island Territories under U.S. administration. 



J,* 







Library of Congress Cataloging in Publication Data: 



Ahlness, Jon K 

In situ copper leaching in the United States. 

(Information circular ; 8961) 

Bibliography: p. 17 

Supt. of Docs, no.: I 28.27:8961. 

1. Copper mines and mining— United States. 2. 
United States. I. Pojar, Michael G. II. Title. III. 
tion circular (United States. Bureau of Mines) ; 8961. 



Solution mining- 
Series: In forma- 



^N295.U4 [TN443.A5] 622s [622\343] 83-600294 






For sale by the Superintendent of Documents, U.S. Government Printing Office 

Washington, D.C. 20402 



CONTENTS 



Page 

Abstract 1 

Introduction 2 

Case histories of operations 2 

Commercial operations with ore body 

preparation 2 

Big Mike Mine 2 

Old Reliable Mine 4 

Zonia mine 6 

Commercial operations in old mine workings. ... 6 

Burro Mountain Branch 6 

Butte, MT, mines 6 

Copper Queen Branch 7 

Inspiration mine 8 

Miami mine 8 

Ohio Copper Co. mine 9 

Ray mine 9 

Experimental programs 10 

Bluebird mine 10 



Page 

Cerrillos deposit 10 

Consolidated Copper Co. mine 10 

Emerald Isle mine 10 

Johnson mine 12 

Kimbley pit 12 

Lakeshore mine 13 

Medler mine 13 

Mountain City mine 13 

Nacimiento mine 14 

Safford deposit 14 

Seneca mine 15 

Sierrita mine 15 

Van Dyke deposit 16 

Summary 16 

References 17 

Appendix A— In situ copper mining 

operating data 18 

Appendix B— Bibliography 21 



ILLUSTRATIONS 

1. Copper in situ mining operation and experimental site locations in the United States 2 

2. Big Mike Mine cross section before and after blast 3 

3. Leaching of terrace at Big Mike Mine 3 

4. Pit bottom leaching at Big Mike Mine 4 

5. Cross section through Old Reliable deposit 5 

6. Old Reliable blasted hillside 5 

7. Solutions collecting at bottom of open pit at Copper Queen Branch 7 

8. Schematic of leaching system at Miami mine 9 

9. Cross section through Ohio Copper Co. mine 9 

10. Prepared surface of blasted cube at Cerrillos deposit 11 

1 1 . Cross section through Emerald Isle mine 1 1 

12. Cross section of Johnson mine deposit 12 

13. Johnson mine test blast design 12 

14. Nacimiento mine well location map 14 

15. Seneca mine blasthole pattern in drift wall 15 

16. Sierrita mine test blast design 15 



TABLES 



1 . Zonia mine blasting data 6 

2. Sierrita mine drill core data 16 

A-1 . Commercial operations 18 

A-2. Experimental operations involving leach solution application 19 



UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT 



IV 



°c 


degree Celsius 


kg/t 


kilogram per metric ton 


m 2 


square meter 


°F 


degree Fahrenheit 


km 


kilometer 


m 3 


cubic meter 


ft 


foot 


kPa 


kilopascal 


md 


millidarcy 


ft 2 


square foot 


L 


liter 


mm 


millimeter 


gal 


gallon 


lb 


pound 


ms 


millisecond 


gpL 


gram per liter 


Ib/d 


pound per day 


pet 


percent 


gpm 


gallon per minute 


lb/ft 


pound per foot 


psi 


pound per square 


gpm/ft 2 


gallon per minute per 


lb/mo 


pound per month 




inch 




square foot 


Ib/T 


pound per short ton 


t 


metric ton 


in 


inch 


Lpm 


liter per minute 


T 


short ton 


kg 


kilogram 


Lpm/m 2 


liter per minute 


yd 3 


cubic yard 


kg/d 


kilogram per day 




per square meter 


yr 


year 


kg/mo 


kilogram per month 


m 


meter 







IN SITU COPPER MINING IN THE UNITED STATES: 
CASE HISTORIES OF OPERATIONS 



By Jon K. Ahlness 1 and Michael G. Pojar 1 



ABSTRACT 



The copper industry has had a long and interesting history associated with leaching, 
involving vat, dump, heap, and in situ methods. The Bureau of Mines has also had an 
interest in copper leaching and has researched the techniques of solution recovery, par- 
ticularly concentrating on in situ methods. In situ mining is a relatively low cost method 
and has been proven commercially successful by nine operations. It has been most com- 
monly used for final recovery in old workings at the conclusion of conventional mining 
operations. 

This report brings together information about 10 commercial in situ operations as well 
as 14 experimental projects. These 24 sites comprise most of the in situ copper mining 
activities that have taken place in the United States. Background information, geology, 
ore preparation, solution application, and recovery and processing are provided for each 
operation. Production data and tables summarizing the engineering statistics for each 
operation and an extensive in situ mining bibliography are included. 



'Mining engineer. Twin Cities Research Center, Bureau of Mines, Minneapolis, MN. 



INTRODUCTION 



The purpose of this Bureau of Mines report is to sum- 
marize the documented in situ copper leach mining activities 
that have taken place in the United States. It was prepared 
to provide a source of engineering and operating data upon 
which future in situ copper mining activities can be based. 
Twenty-four different sites are discussed. These are all of the 
sites that are known to the authors from the extensive in situ 
copper leach mining bibliography developed at the Bureau's 
Twin Cities (MN) Research Center (Appendix B). 

In situ copper leach mining activities fall into the follow- 
ing categories: 

1. Commercial operations with ore body preparation. 

2. Commercial operations in old mine workings. 

3. Experimental programs. 

Ore body preparation includes such activities as blasting, 
block caving, and hydraulic fracturing (hydrofracing) 
specifically to fragment the ore body. Operations in old mine 
workings include those done in open pits, worked out block 
caved areas, and backfilled stopes where leaching is done 
as an afterthought to conventional mining. Experimental pro- 
grams are small-scale tests of the feasibility of a commercial 
operation. Some of these programs did not progress to the 
point where leach solutions were applied to the ore. 

Each operation (locations shown in figure 1) will be 
discussed in terms of background information, geology, ore 
preparation, solution application, recovery and processing, 
and engineering and production data. Information was col- 
lected from published reports, communications with company 
personnel, and site visits. 

In situ mining and the chemistry of leaching copper 
minerals have been previously discussed (3, 17, 19, 21, 33), 2 
however, some basics will be covered. 

After a suitable leach solution chemistry has been deter- 
mined, the solutions must be exposed to as much mineraliza- 
tion as possible. This means the ore body must have 
adequate permeability, either natural through fractures or in- 
terconnected pore spaces, or induced by blasting, caving, 
or hydrofracing. The solution must then be evenly applied 
to the ore. This can be done with rotating head sprinklers, 
perforated pipes, lengths of surgical tubing known as Bagdad 
wigglers, injection holes, or ponds. A method for collecting 
the pregnant solutions is then needed. This has typically been 
done with recovery wells, or underground mine workings 
(raises, ore chutes, and drifts) that direct the solutions to a 
sump. Pregnant solutions are then treated to remove the 
values. In the case of copper, treatment is done by precipita- 
tion on scrap iron or solvent extraction-electrowinning 
(SX-EW). In either case, effluent solution from the plant can 
be recycled back to the leach area. 

Because copper-bearing deposits vary considerably in 
shape, form, and geology, no single method of leaching is 
universally applicable. Regardless of the preparation method 



to leach copper successfully the following requirements must 
be met: 

1. Non-acid-consuming host rock. 

2. Host rock that will not decrepitate to seal intrarock 
fractures and block solution flow. 

3. Rock sufficiently fractured to permit access of solu- 
tion to copper minerals. 

4. Copper minerals concentrated largely along frac- 
tured planes of rock. 

5. A solid impervious surface under or surrounding the 



deposit 
6. 

limits. 
7. 



Copper minerals that dissolve within required time 



Ability to recirculate the solution through the ore 
many times without excessive loss or contamination. 

8. Availability of adequate water. 
In situ leach mining is a method that can be used to max- 
imize resource recovery at an economical cost. 



• Seneco mine 
(Mohawk, MI, 
not shown) 




Big 

Mike 

Mine 
Mountain 
City mine 
Kimbley pit 
Consolidated _ 
Copper Co. mine 



Old Reliable 
Mine 

Sierrita mine 



• Nacimiento mine 
• Cerrillos deposit 



Miami, Inspiration, | 

Bluebird mines, Van Dyke deposit 

Medler mine 
I 

"""—Burro Mountain 
Safford Branch 

deposit 
Johnson mine 
Copper Queen 
Branch 



Figure 1 .—Copper in eltu mining operation and experimental 
site locations in the United States. 



CASE HISTORIES OF OPERATIONS 



COMMERCIAL OPERATIONS WITH 
ORE BODY PREPARATION 

This section includes all commercial in situ ventures 
where ore was prepared for leaching by blasting. Included 
are the Big Mike Mine, initially an open pit, the Old Reliable 
Mine, initially an underground operation, and the Zonia mine, 
initially an open pit-heap leaching operation. The Old Reliable 
used a "coyote" blast to fragment ore and overburden, and 
the Big Mike and Zonia used vertical and angled blast holes 



italicized numbers in parentheses refer to items in the list of references 
preceding the appendixes. 



to fragment ore. All three operations started leaching during 
the 1972-74 period, but are currently inactive. 

Big Mike Mine 

The Big Mike Mine is located approximately 30 miles (48 
km) south of Winnemucca in Pershing County, NV. Interest 
in the property dates from the 1900's, however, little explora- 
tion was undertaken until the mid-1 960's. Ranchers Explora- 
tion and Development Corp. obtained the property in 1969 
and began a drilling program to confirm earlier exploratory 
results. The deposit was determined to contain reserves of 
about 100,000 T (90,720 1) of 10 pet massive copper sulfide 






ore and 700.000 T (635,030 t) of 2 pet mixed oxide-sulfide 
ore. The massive sulfide mineralization consisted of 
chalcocite and chalcopyrite. and the mixed ore included 
cuprite, tenorite. and chalcopyrite. The deposit was approx- 
imately 600 by 300 ft (1 83 by 92 m). and extended to a depth 
of 300 ft (92 m) from the surface (38). 

Initial open pit mining began in January of 1970. and by 
midyear 100.000 T (90.720 t) of the high-grade sulfide ore 
had been mined along with 300.000 T (272,160 t) of low-grade 
mixed ore. The high-grade material was shipped to market. 
The low-grade material was stockpiled, and in late 1971 it 
was crushed to minus 2 in (51 mm), stacked on an 
impermeable asphalt pad, and heap leached (38). 

As a consequence of this method of mining, approx- 
imately 475,000 T (430.900 1) of low-grade mixed oxide-sulfide 
ore was left in the walls and the bottom of the pit. It was 
decided in mid-1972 to blast this remaining ore into the pit 
and to leach it in place. Open pit mining had been con- 
templated, however, it would have required a 6.5:1 stripping 
ratio and the economic rate of return was considered to be 
unacceptable {38). 

On July 10, 1973, 640,000 T (580,600 t) of copper ore 
and waste rock (average grade of 1.18 pet Cu) was blasted 
into the open pit using 400.000 lb (181,440 kg) of ammonium 
nitrate-fuel oil (AN-FO) and waterproof slurry explosives (38). 
One hundred and seventy-five blastholes were drilled around 
the perimeter of the pit and another 75 in the pit bottom. Three 
sizes were drilled— 5.75-, 9-, and 9.875-in-diam (146-, 229-, 
and 251-mm). Hole spacing was a 10- by 10-ft (3- by 3-m) 
pattern for the small holes and a 20- by 23-ft (6- by 7-m) pat- 
tern for the large holes. The perimeter holes were up to 300 
ft (92 m) deep and angled up to 35°, and the pit bottom holes 
were up to 100 ft (31 m) deep (38). The ore and waste were 
reduced by blasting to pieces averaging about 9-in diam (230 
mm). The shattered ore and waste were then leveled in 
preparation for leaching. A cross section of the pit before and 
after blasting is shown in figure 2. 



Preshot 




Blastholes 



Blast limit hne 



Figure 2.— Big Mike Mine cross section before and after 
blast. 

Leaching was carried out by sprinkling a dilute solution 
of H 2 S0 4 on the ore with Rainbird 3 sprinklers as shown in 
figures 3 and 4. A water table was present near the bottom 
of the pit. It was assumed that this coupled with impermeable 
pit walls would act as a barrier to the percolating solution. 

Solution recovery involved one production well drilled 
through the blasted zone in the pit bottom. A 175-gpm (660 
Lpm), 10-stage stainless steel submersible turbine pump was 
used to pump the pregnant leach solutions to the precipita- 
tion plant. Recovery was assisted by the area water table, 
which was 50 ft (15 m) above the pump. Pregnant leach solu- 
tion grade averaged 1.0 gpL and did not vary with 
temperature changes. 



Reference to specific equipment does not imply endorsement by the Bureau 

of Mines. 




Figure 3.— Leaching of terrace at Big Mike Mine. 







Figure 4.— Pit bottom leaching at Big Mike Mine. 



Pregnant solutions from the pit bottom were pumped to 
a standard iron launder precipitation plant where they were 
mixed with pregnant heap leach solutions. Cement copper 
was washed from the concrete cells into a decant area. The 
copper was then placed on a concrete drying pad where it 
was turned periodically until the moisture was reduced to an 
acceptable level, before it was trucked to a railhead and ship- 
ped to a Nevada smelter. 

The operation was expected originally to produce 5,000 
Ib/d (2,270 kg/d) of copper for 3 yr. After the initial startup 
in 1973, however, it was shut down in 1974 when the price 
of copper fell. It was started again in 1978 and ran until 1979 
when the solution grade dropped too low to be economic. 
There are no current plans for any further leaching at the 
mine. The operation was economically very successful; 
development costs were recovered in 6 months. Total cement 
copper production from both heap and in situ was 7 million 
lb (3,175,000 kg) which represented a 25-pct recovery. 
Operating data are summarized in table A-1. 

Old Reliable Mine 

The Old Reliable Mine is located 40 miles (65 km) north- 
east of Tucson, AZ, in the Copper Creek area of the Galiuro 
Mountains. The site is located on ground that was first 
claimed for its mineral value during the Civil War. Old Reliable 
was mined sporadically as an underground operation from 
1890 to 1919. During the period it yielded approximately 
30,000 T (27,200 1) of ore (78). Except for one additional short 



time span between 1953 and 1954, the deposit had gone 
unmined for half a century. The amount of ore contained in 
the deposit made further conventional mining economically 
unfeasible. In 1970 the deposit came under control of 
Ranchers Exploration and Development Corp. 

The ore body is a near vertical breccia pipe (fig. 5). The 
host rock is andesite, a lava that is the principal rock in the 
Glory Hole Volcanic Formation. Molten granite intruded on 
the area of the deposit perhaps 68 million years ago and 
cracked the volcanic rock. Copper-bearing solutions flowed 
into the cracks and voids in the brecciated lava. Ground water 
later dissolved and redeposited the copper deeper in the ore 
body in concentrated form. The deposit extends from the 
surface to a depth of 500 ft (152 m). That portion near the 
surface is low-grade, containing less than 0.4 pet copper. 
Mineralization increases with depth, however, reaching an 
average grade of about 2 pet Cu near the bottom of the ore 
body. High-grade areas within the deposit sometimes reach 
9 to 10 pet (11). The deposit is sized at 4 million T (3.6 X 10 6 1) 
of ore averaging 0.84 pet Cu with a 70:30 sulfide-oxide ratio. 
The most abundant copper minerals are chalcocite, 
malachite, chalcopyrite, and chrysocolla. 

Ranchers Exploration and Development Corp. decided 
that a combination of blasting and leaching could be used 
to recover copper values. After a thorough investigation of 
the ore body, E. I. du Pont de Nemours & Co. recommended 
a "coyote" type blast. In contrast to the conventional method 
of drilling vertical blastholes, a coyote shot uses a network 
of tunnels and crosscuts driven into the deposit. 




Figure 5.— Cross section through Old Reliable deposit. 

The Old Reliable contained 4,000 ft (1 ,220 m) of tunnels 
and crosscuts from previous mining, and an additional 4,000 
ft (1,220 m) of tunneling was driven for the blast. It was 
calculated that 4 million lb (1,814,370 kg) of explosives was 
required for the blast. Eighty thousand 50-lb (23-kg) bags of 
AN-FO were placed in the tunnels and crosscuts. A wired 
system of blasting caps, detonating cord, and high-explosive 
primers was connected to the detonation station in a bunker 
about a mile from the blast site. The explosive charges were 
confined by blowing sand into the tunnels and crosscuts and 
by placing bags of sand for stemming. On March 9, 1972, 
the shot was fired. Breakage of the ore was considered 



excellent with pieces averaging approximately 8.5-in diam 
(216 mm) (32). The blast fractured a total of 5 million T (4.5 
X 10 6 t) of material averaging 0.78 pet Cu. 

Terracing of the fragmented deposit with a bulldozer was 
completed by May 30, 1972. Figure 6 shows the blasted 
hillside. A total of 50 million gal (18.9 X 10 7 L) of leach solu- 
tion was required to saturate the fractured ore body. To pro- 
vide water to soak the leach area, a 17.5-in-diam (445-mm) 
well was drilled at a location about 6 miles (9.66 km) from 
the plant site. The water was acidified with H 2 S0 4 at the plant 
in a barren-solution pond before it was applied to the ore. 

A sprinkler system was developed for applying the solu- 
tion. Two distribution systems existed, each comprised of one 
6-in-diam (152-mm) main transmission line and several 2-in- 
diam (51 -mm) distribution lines. Rotating sprinkler heads were 
spaced at 40-ft (12-m) intervals along the distribution lines. 
The sprinklers were plastic bodied with stainless steel pins 
and rings. The front and rear spray nozzles covered a cir- 
cular area with a radius of 60 ft (18 m) (18). 

By September, solution was being sprayed on the 
fragmented ore at a rate of 400 gpm (1,514 Lpm), and pro- 
duction of copper began in January 1973. At full capacity, 
solution was fed at 1 ,000 gpm (3,785 Lpm) to the leaching 
sites to provide 800 gpm (3,028 Lpm) of pregnant liquor for 
the plant; the difference was lost to evaporation. Design pro- 
duction capacity of the operation was approximately 20,000 
Ib/d (9,072 kg/d) of copper. Production life was expected to 
be roughly 5 yr. 

Pregnant leach liquors flowed from the base of the rub- 
blized hillside just above the water table into a catchment 
basin. From there the leach liquors flowed first to a retention 
pond, then to the cementation launders where the pregnant 
copper solution was precipitated onto incinerated scrap iron. 
Six concrete, false-bottomed launders, 8 by 24 ft (2.44 by 
7.32 m) were used. Copper precipitated on the iron, in 98-pct 
conversion, was sluiced off once a day by high-velocity water 
streams. The settled out copper was periodically removed 




Figure 6.— Old Reliable blasted hillside. 



onto a solar drying pad. The cement copper, approximately 
80 pet Cu on a moisture-free basis, with the balance com- 
prised largely of oxygen, iron, and silica, was shipped to 
smelters for refining. 

The Old Reliable was leached for 2 yr until September 
1 974, with recovery estimated at 1 pet the first year and 6 
pet the second. At that point the dwindling solution grade (0.8 
gpL) and a falling copper price dictated shutdown. In August 
1979 leaching of the site resumed. Six injection holes sup- 
plied an acid leach solution at a rate of 300 to 350 gpm (1 ,1 35 
to 1,325 Lpm). A similar amount of leach solution was 
distributed through the sprinklers. Application of leach solu- 
tion was discontinued again in September 1980, and cement 
copper production ceased in January 1981 , when Ranchers 
Exploration could not extend the property lease. At the time 
of shutdown the solution grade was 0.4 gpL Cu. 

Total copper recovery during the life of the in situ opera- 
tion was 13 million lb (5,896,700 kg). This represented only 
1 9 pet of the total copper, but 64 pet of the oxide. A 6-pct 
copper recovery was needed to break even and was achieved 
during the first 6 months of operation. Operating data are 
shown in table A-1 . 

Zonia Mine 

The Zonia mine is located approximately 100 miles (160 
km) northwest of Phoenix near Kirkland, AZ. The Zonia mine 
has been in existence since 1877, but was not operated suc- 
cessfully until it was purchased by the McAlester Fuel Co. 
in 1966. From 1966 to 1972 the operation consisted of an 
open pit and heap leach. In 1972 it was decided that the 
remaining ore reserves would be blasted and leached in situ 
(31). 

The deposit occurred in a host rock that was a Precam- 
brian shale and andesite mixture. The major copper-bearing 
mineral was chrysocolla, which was disseminated throughout 
the ore body. Minor amounts of azurite, malachite, and 
tenorite were also present. The ore grade averaged less than 
0.3 pet Cu. 

Three blasts were detonated between April 1973 and 
May 1 974 to fragment the ore for leaching. Holes for the first 
blast were drilled to an average depth of 170 ft (52 m). Hole 
spacings ranged from 11 to 15 ft (3.4 to 4.6 m) depending 
on hole depth. Table 1 summarizes the blasting data. 

Dilute H 2 S0 4 was applied at the rate of 0.0017 to 0.0025 
gpm/ft 2 (0.07 to 0.10 Lpm/m 2 ). Application methods included 
sprinklers and perforated pipes. Leach solutions collected at 
the base of the ore body and were pumped to the surface 
through a recovery well. The water table was used as an aid 
for leach solution collection. Pregnant solutions were 
processed in a precipitation plant that had a maximum pro- 
duction capacity of 5,000 lb (2,270 kg) of copper per day. In 
the 2 yr of operation, approximately 10 pet of the copper from 
the broken ore was recovered. 

The Zonia closed in early 1 975 because of the low price 
of copper and a lack of a market for the product, cement cop- 
per. The McAlester Fuel Co. was later purchased by another 
energy fuels company, and the mine was put up for sale. 
Reserves containing 0.3 pet Cu still remain. Table A-1 sum- 
marizes the in situ mining operation data. 



Table 1 .—Zonia mine blasting data 





9-in-diam blastholes 


Explosive 


Ore 


Date 


Num- 
ber 


Depth, 
ft 


Type 


Amount, 
10 3 lb 


blasted, 
10 3 T 


Apr. 1973 ... 
Mar. 1974 .. . 

May 1974 . . . 


1,710 
NA 

754 


100-240 
NA 

110-212 


AN-FO . . . 
AN-FO, 
slurry. 
...do ... 


4,140 
873 

1,544 


4,000 
1,050 

1,780 



NA Not available. 



COMMERCIAL OPERATIONS IN OLD 
MINE WORKINGS 

In situ mining in old mine workings is discussed in this 
section. No ore preparation was done; leaching was an after- 
thought to conventional mining. Of the seven operations in 
this category, five involved the leaching of old block caved 
workings, one involved backfilled stopes, and the other, an 
open pit with underground workings; two are currently active 
(Copper Queen Branch and Miami mine). 

Burro Mountain Branch 

The Burro Mountain Branch of Phelps Dodge Corp. was 
located 10 miles (16 km) south of Silver City, NM, at the pre- 
sent site of Tyrone. Phelps Dodge acquired the property in 
1909 and mined 2 million T (1 .8 X 10 6 1) of ore by underground 
methods before the mine closed in 1921 (30). The principal 
copper mineral was chalcocite. 

In May 1941 , in situ mining of old low-grade caved areas 
began. Water was percolated through the caved material, col- 
lected underground, and the pregnant solution processed in 
a precipitation plant (34). The plant and leaching operations 
were expanded in 1942 (30). Leaching was interrupted by 
strikes in 1946 and 1948 and was finally discontinued in 1949 
(30). The area is now part of the Tyrone open pit. Operating 
data are shown in table A-1. 

Butte, MT, Mines 

In situ copper mining has been done in the old backfilled 
stopes of the Anaconda Minerals Co. underground mines 
near Butte, MT, since the 1930's. The practice evolved from 
the work of the "fire fill" crew. This crew drilled holes into 
old stopes and flooded them to extinguish fires. They found 
that the water disolved significant amounts of copper. In situ 
leaching was eventually done in three of the six major 
underground copper mines in the area (Leonard, Mt. Con, 
and Steward). In 1964, all in situ leaching activities in the area 
terminated with the introduction of dump leaching, which pro- 
duced higher grade solutions and accounted for the entire 
capacity of the solution processing plant. The last of the 
underground mines closed in 1981 , and the Berkley Pit closed 
in May 1982 (20). 

The host rock for the ore is a quartz monzonite. Prin- 
cipal copper minerals are chalcopyrite and chalcocite with 
minor amounts of bornite, azurite, and malachite. The ore 
occurs in veins that typically dip at 60°. The underground 
mine workings extend to 5,000 ft (1 ,525 m) in depth, but most 
of the leaching was done in the upper 3,000 ft (900 m). Stopes 
were typically 100 to 150 ft (30 to 46 m) high and 75 ft (23 
m) in strike length on both sides of a center service raise. 
They were backfilled with mine waste that typically graded 
0.8 pet Cu, but occasionally as high as 2.0 pet. 

Two leaching methods were used, flooding and trickle 
leaching. Flooding produced the most favorable results. 
Bulkheads were built to isolate stopes, which were then 
flooded with water through old mining access points. The 
stope was filled to the top, drained immediately and allowed 
to sit for at least 2 months before being flooded again. During 
the rest period, compressed air was pumped into the stopes 
to increase oxidation of the material. 

Trickle leaching was done by drilling injection holes into 
the stopes from the hanging wall. The holes were positioned 
to allow the leach solution to contact the greatest amount of 
ore before it flowed down along the footwall. An injection rate 
of 3 gpm (1 1 Lpm) per hole was used. Higher rates caused 
channeling. Leach and rest cycles ranged from alternate 
months to continuous leaching until the grade dropped to an 
unacceptable level (usually 2 to 3 months) before resting. 
Pregnant solutions from each level area were monitored, with 
the arbitrary cutoff depending on grades from several 
locations. 






The first leach solution used at Butte was surface water. 
Eventually water pumped from the mine for dewatering pur- 
poses was used. This water was more effective because its 
ferric sulfate content aided the leaching process. Total flow 
rate to the stopes never exceeded 700 gpm (2,650 Lpm). 
Small amounts of H 2 S0 4 were added underground to lower 
the solution pH to 2.1 from 2.7, which prevented iron salt 
precipitation. The total number of stopes under leach at one 
time depended on the other operations in the mine. Most 
leaching was done when the mine was on a reduced produc- 
tion schedule so the leaching would cause only minimum 
interference. 

Pregnant leach solutions mixed with other mine water 
in the mine sump. This mixture was pumped at a rate of 5,000 
gpm (19.000 Lpm) to the precipitation plant on the surface, 
the mixed solution contained 0.50 to 0.75 gpL Cu. Operating 
data are shown in table A-1 . 

There is still substantial leaching potential in the old 
stopes, but conventional underground mining would have to 
be justified, because, while in situ mining more than paid for 
mine dewatering, it was not economic on its own. 

Copper Queen Branch 

The Copper Queen Branch of Phelps Dodge Corp. is 
located at Bisbee. AZ. The area has a copper mining history 
dating back to the 1880's when production from the mine 
began. Phelps Dodge bought the Copper Queen in 1885 and 
operated the underground mine relatively uninterrupted until 
June of 1975 when low copper prices and high labor costs 
caused it to be shut down. Phelps Dodge began production 
from the Lavender Pit in 1954 and operated it for 20 yr until 



its closure in December of 1974 (29). In situ mining of the 
Lavender Pit, with the solution collected in the underground 
workings of the Copper Queen, began in 1975 to supplement 
the dump leaching that had been done since the late 1950's. 
In situ mining was an economical way to recover more copper 
from the pit. Both the dump and in situ leaching operations 
are currently active. 

The host rock for the ore in the Lavender Pit is the 
Sacramento quartz porphyry stock. The principal copper 
mineral is chalcocite, with minor amounts of azurite and 
malachite. No ore preparation was done in the pit before leach 
solutions were applied. 

The water used for leaching in the Lavender Pit is 
pumped from the underground mines. No acid is added 
because it is generated from the oxidation of pyrite in the ore. 
The water is sprayed onto the pit walls with approximately 
70 sprinklers. Each sprinkler covers a radius of about 35 ft 
(1 1 m), but radius of coverage varies slightly with the depth 
of the sprinkler in the pit. The sprinklers have no pattern or 
set spacing, but are placed on exposed ore where access 
is available to personnel. All the accessible areas are 
presently being leached, and the cost to open more areas 
is prohibitive. No leach-rest cycle is followed. 

Solutions run down the walls and collect at the pit bottom 
(fig. 7), 950 ft (290 m) below the surface. Two holes drilled 
in the pit bottom provide passage for the copper leach solu- 
tions to the underground workings. The solutions then migrate 
down to the 1 ,800-ft (549-m) level where they collect and are 
pumped to the surface through the Junction shaft. They are 
mixed with pregnant solutions from the No. 7 dump before 
treatment in a precipitation plant. The barren solution from 
the plant is recirculated to the No. 7 dump. 



■I 



** 










,»« 







Figure 7.— Solutions collecting at bottom of open pit at Copper Queen Branch. 



In situ mining has also been done in the nearby Camp- 
bell underground mine. The 1,400-ft (427-m) level was 
dammed and flooded. Solutions percolated down to the 
2,100-ft (645-m) level and were pumped to the solution col- 
lection area in the Junction Shaft before being pumped to 
the surface. . 

The copper grade of the mixed solution fed to the cemen- 
tation plant is 0.6 gpL. Total copper production capacity is 
about 24,000 Ib/d (10,896 kg/d) with the in situ portion con- 
tributing about 25 pet. Labor requirements for the operation 
are small. Two individuals can handle the pit's plumbing and 
only minimal maintenance is needed in the underground 
workings. Sprinkler plugging is not a problem, because none 
of the barren solution is recirculated back to the pit. The 
leaching is planned to continue as long as the pregnant solu- 
tions grade remains satisfactory. Operating data for the in 
situ mining program are shown in table A-1. 

Inspiration Mine 

The Inspiration mine is located between the towns of 
Miami and Globe, AZ, about 75 miles (120 km) east of 
Phoenix. The mine, owned by Inspiration Consolidated Cop- 
per Co., was originally a block caving operation but is 
presently active as an open pit. Dump leaching began in 1950 
on waste material that was stripped from the pit. In situ mining 
of portions of the old, block-caved workings was done from 
1967 to 1974. 

The host rock for the ore is a granite schist. The prin- 
cipal copper minerals are azurite, malachite, and chrysocolla 
with minor amounts of chalcopyrite, chalcocite, cuprite, and 
covellite. The ore grade in the block-caved workings at the 
time of leaching was below 0.5 pet Cu. The leach area was 
above the water table. 

Preliminary work began around 1965 with the drilling of 
injection holes. Approximately 30 holes were drilled in a 3- 
to 4-acre (12,140 to 16,187-m 2 ) area and were cased with per- 
forated plastic pipe. This area was near Inspiration's prop- 
erty boundary and could not be included in the open pit opera- 
tion without extending the pit onto the neighboring property. 
This left in situ leaching as the only economic alternative for 
recovering more copper from the caved area. 

Leach solution was effluent solution from the precipita- 
tion plant with 6 to 10 gpL H 2 S0 4 added. Solution injection 
started in 1967 and ranged from 5 to 20 gpm (19 to 76 Lpm) 
per hole. There was no specific timetable for leach-rest cycles. 
When the grade from an area dropped below the cutoff level, 
the area was rested 3 to 5 months. The average pregnant 
solution grade dropped gradually during the operation. 

Solution application was originally handled by four per- 
sons working 8-hour shifts, 5 days per week. Their respon- 
sibilities were to check solution flows to the weir boxes and 
to keep acid tanks full. The crew size was eventually cut to 
one. 

The pregnant solutions migrated down through the caved 
ore and collected in drifts at the 850-ft (260-m) level. They 
were then pumped up the shaft to the precipitation plant. The 
plant consumed 200 T (1 80 1) of scrap iron each month. Cop- 
per production averaged 1 .9 million lb (8.6 X 10 5 kg) per year 
during the operation. 

Leach solution was no longer applied after 1974 for the 
following two reasons: 

1 . The automatic pump malfunctioned and flooded the 
pump station. 

2. An agreement was made with the neighboring 
property owners to allow Inspiration to extend its open pit onto 
their land. This allowed the area to be mined as an open pit. 

The operation had no major problems. Iron salt buildup 
was controlled by adjusting the leach solution pH. Solution 
channeling was handled by shooting small explosive charges 
in the wells to "shake up" the material around the wells to 
change flow patterns. 

Although in situ mining is not now taking place at Inspira- 



tion, dump leaching still is. New material is continuously being 
added to the leach dumps from the open pit stripping, and 
a new SX-EW plant was built in 1979. Operating data for the 
in situ mining program are summarized in table A-1. 

Miami Mine 

The Miami mine is located near Miami, AZ, about 70 
miles (112 km) east of Phoenix; production from it began in 
1910. The original ore body averaged 2.0 to 2.5 pet Cu and 
was mined by sublevel caving and shrinkage stoping 
methods; however, the principal mining method used for the 
large quantities of lower grade ore was block caving (13). By 
1928, 100 million T (90.7 X 10 6 t) of ore graded at 0.88 pet 
sulfide copper had been delineated for block caving (23). All 
conventional mining ended in June of 1959 after 152.4 million 
T (138.3 X 10 6 1) of ore had been mined and the ore body 
had been exhausted. In situ mining of the caved stopes began 
on a small scale in a worked out portion of the mine in January 
of 1942, with full-scale leaching beginning when the 
underground mine was closed in 1959 (13). 

The host rock for the deposit is the Precambrian Pinal 
Schist, which has been intruded by the Schultz Granite 
porphyry, and is partially covered by the Gila Conglomerate. 
The area is highly faulted and fractured. The principal cop- 
per mineral is chalcocite with minor amounts of chalcopyrite, 
bornite, covellite, malachite, azurite, chrysocolla, cuprite, and 
native copper. The mineralization occurs in seams, veinlets, 
and disseminated particles. Reoxidation of the enriched 
sulfides along two major faults produced some mixed oxide- 
sulfide ore (13). 

Block caving of the ore body was done on a checker- 
board pattern with blocks being 150 by 150 ft (46 by 46 m) 
and 150 by 300 ft (46 by 92 m). The caving activity resulted 
in surface subsidence over a 5-million-ft 2 (4.6 X 10 5 -m 2 ) area 
creating a "glory hole" 600 ft (183 m) deep. The resulting 
material left to be leached is 600 ft (183 m) of ore and waste, 
with the prime leaching target being the bottom 150 ft (46 
m). The overlying material only averaged 0.03 pet copper (13). 

Besides leaching the leftover caved material, two 
attempts were made to prepare ore specifically for leaching. 
In 1954, a low-grade portion of the ore body was block caved 
with just enough draw to break the ore to the surface (9), and 
in 1969 another low-grade portion was mined as an open pit 
with the ore placed in the glory hole. This involved 1 .3 million 
T (1.2 X 10 6 t) of material grading 0.78 pet. It created a 
leaching pad area of 200,000 ft 2 (18,580 m 2 ) that was 135 
ft (41 m) thick (13). 

The first attempt at leaching in 1 942 was done with water, 
but it proved unsuccessful because not enough pyrite was 
present in the ore to generate the needed acid. A 6.0-gpL 
H 2 S0 4 solution was then tried successfully. Solution has been 
applied with sprays, ponds, and injection holes, but only 
sprays and holes are currently used. Ponding was discon- 
tinued because it applied the solution at too fast a rate and 
because of the leach area's unevenness. 

Sprays are created with perforated plastic pipes, which 
are 2-in diam (51 -mm) and are punched with an ice pick every 
6 to 8 ft (1 .8 to 2.4 m). The pipes are placed on terraced areas 
of the glory hole. These areas have to be reworked period- 
ically when the solution percolation slows or the grade drops 
off. Reworking is done by bulldozing about 3 ft (1 m) of 
material off the surface and over the edge. 

Injection holes are 6-in diam (152-mm), average 195 ft 
(60m) deep, and are cased with 2-in-diam (51 -mm) PVC pipe, 
perforated in the bottom portion. A 1-in-diam (25-mm) hose 
carries the solution from the plastic distribution lines to the 
casing. 

Flows to different leach areas are controlled by weir 
boxes where acid is added to bring the acid concentration 
level up to 5.0 gpL. Both sprays and injection holes are fed 
from an individual weir and, because flow rate is measured 
only at the weir, the flow into individual holes is undetermined. 



Five hundred holes were in use in June 1981 and more were 
being drilled. Some of these have been used for years and 
still accept as much solution as is normally injected, while 
the flow to others has to be reduced to a trickle to prevent 
overflow. The maximum area of influence from an injection 
hole is assumed to be a circle 50 ft (15 m) in diameter. 

Leach solution percolates down from the surface through 
the caved ore and then through raises and drawpoints until 
it reaches the 1,000-ft (305-m) level, which was the final 
haulage level. This percolation usually takes 3 to 4 weeks 
from the time solutions are applied at the surface and lasts 
2 weeks after application stops. Two drifts on the collection 
level run under the ore body. Dams in these drifts contain 
the pregnant leach solutions. Pipelines [16-in diam (406-mm)] 
carry solutions from the dams to the sump which is 120 ft 
(37 m) deep. Automatic shutoff valves prevent solution in the 
sump from rising too high and flooding the pump station. 
There are 41 underground sampling points for monitoring the 
leach solution grades. Leach solutions from the mixed oxide- 
sulfide ore areas have higher grades than those from sulfide 
areas (12). 

Solutions are pumped through 12-in-diam (305-mm) 
stainless steel pipe to the SX-EW plant on the surface by three 
1.000-gpm (3,785-Lpm) stainless steel submersible pumps, 
with a fourth pump as a backup. The pumps are placed in 
casings in the sump. The SX-EW plant was built in 1976. 
Previous to this, a precipitation plant designed to produce 
50,000 Ib/d (22,700 kg/d) of cement copper was used. The 
SX-EW plant was designed to handle 3,000 gpm (1 1 ,350 Lpm) 
of pregnant leach solution, and to produce 30,000 to 35,000 
lb (13,600 to 15,900 kg) of cathode copper per day. 

Solutions grades from the initial leaching were 4.2 gpL 
Cu. In 1963, the time when there were no more new areas 
to leach, the grade had dropped to about 2.0 gpL and by June 
of 1981 the pregnant solution grade was 0.85 gpL. Copper 
recovery by solvent extraction is approximately 90 pet. 
Temperature of the pregnant leach solution to the SX-EW 
plant is a constant 69 ' to 71 ° F (20 ° to 22 ° C), which is ideal 
for processing. Total copper production through 1981 by in 
situ mining at Miami was about 275 million lb (125 X 10 6 kg). 

The operation currently employs approximately 40 
people including management, maintenance, and a 
10-person underground crew that keeps the old workings 
open and collects samples. The life expectancy of the in situ 
leaching operation is uncertain but to this point has been very 
successful and profitable. A schematic of the operation is 
shown in figure 8 and a summary of operating data is given 
in table A-1. 

Ohio Copper Co. Mine 

The Ohio Copper Co. mine was located in Bingham 
Canyon, UT, about 20 miles (32 km) southwest of Salt Lake 
City. In situ copper leaching took place in the 1920's after 



/££/- 3-"> poiyein,iene 
Ht , ' ptothc pee 



Solution er'e'j ground 




I ^ ... 

* Hanging wall quartzite 
\(Broken up due to mining 
> operations) 




Tunnel level 



Figure 8.— Schematic ot leaching system at Miami mine. 



Figure 9.— Cross section through Ohio Copper Co. mine. 



the block caving operation shut down when the veins on 
which mining operations originally depended were more or 
less completely worked out (1). 

The host rock for the ore body was quartzite and quartz 
monzonite. The principal copper mineral was chalcocite which 
was disseminated throughout. Azurite and malachite were 
present in minor amounts. The average grade of the 
estimated 38 million T (34.5 X 10 6 1) in the caved area was 
0.3 pet Cu (40). Pyrite was also present. The caved zone was 
in the shape of a truncated cone with the 1,200-ft (366-m) 
axis 40° off the vertical (fig. 9). The upper dimensions of the 
cone were 1 ,400 by 600 ft (427 by 183 m). The bottom area 
was about one-fourth of the top (1). 

In August of 1922, 250 gpm (946 Lpm) of water from 
Bingham Canyon Creek was applied to the surface of a sump 
over the caved area. The solutions that collected in the 
underground workings contained 4.5 gpL Cu. With the suc- 
cess of this program, solutions were being applied at a rate 
of 1 ,200 to 1 ,400 gpm (4,542 to 5,300 Lpm) by November 
of 1923 when mine water was used to supplement the creek 
water (1). Leach solutions were distributed by a 150-ft (46-m) 
long launder built of three 2- by 12-in (51- by 305-mm) planks 
with 2-in (51 -mm) holes in the sides. The launder was moved 
on a regular pattern. Later, cascading was attempted to try 
to introduce oxygen into solution (6). 

The solutions percolated through the broken material and 
then through ore chutes to a tunnel 700 ft (214 m) below the 
bottom of the caved area. The pregnant solutions were proc- 
essed in a precipitation plant in the tunnel. Copper produc- 
tion was 600,000 lb/mo (272,400 kg/mo), and the plant 
recovered 97 pet of the copper from solution. Operating data 
are shown in table A-1. 

Ray Mine 

The Ray mine is near the town of Ray, AZ, about 70 miles 
(1 1 2 km) southeast of Phoenix. The host rock for the ore body 
is schist porphyry. The principal copper mineral in the ore 
mined by block caving was chalcocite; it averaged 1.0 pet 
Cu and was the result of secondary enrichment. Pyrite con- 
tent was very high. Above the ore was 125 ft (38 m) of low- 
grade material averaging 0.6 pet copper, and 50 ft (15 m) of 
barren capping that ran to the surface (37). 



10 



The mine closed in 1933 and did not reopen until 1937. 
This allowed the broken ore that remained in the block cave 
to oxidize to the point where it was difficult to mill (12). Since 
no further mining operations were planned on lower levels, 
it was decided to leach the remaining material in situ. 
Drainage drifts were driven, concrete dams were installed to 
prevent the solution from flowing into working areas, and a 
concrete ditch with a 500-gpm (1 ,900-Lpm) capacity was built 
to carry pregnant solutions to the pumping station. 

Water was first applied to the caved surface on January 
20, 1937, using rotary head sprinklers. The leach area 
covered about 10 acres (40,500 m 2 ) although the entire area 
was not leached at one time. Pregnant solution grades would 
decrease with time when the sprinklers were left in one loca- 
tion. It was found, however, that by moving the sprinklers, 
letting the area rest, and then releaching, the solution grades 
would return to higher levels. The standard pattern would be 
to leach an area until the solution grade dropped to 4.0 gpL 
and then rest the area for 2 months. When solutions were 
reapplied, the grades would return to 10.0 gpL (12). 

After 6 months of leaching, substantial settlement of the 
caved area destroyed the solution distribution pipeline 
system. Leach solution was then only applied to the edges 
of the caved area with a few hose lines run into the cave. 

Pregnant solutions collected underground and were 
pumped to the surface through an 8-in-diam (200-mm), lead- 
lined pipe. Processing was done by precipitation on scrap 
iron in a plant designed to handle 500 gpm (1 ,900 Lpm). The 
plant was operated by six people during the day shift only. 
All tailing solution was discarded. In the first 18 months of 
operation, 10 million lb (4.5 X 10 6 kg) of copper was produced 
from pregnant solution with an average grade of 9.23 gpL 
(36). Operating data are shown in table A-1 . The in situ leach 
area is now part of the Ray open pit, where present activities 
are open pit mining and dump leaching. 



EXPERIMENTAL 
PROGRAMS 

Experimental leaching programs and fragmentation tests 
are discussed in this section. Such programs are typically 
small scale and are used to determine the feasibility of a com- 
mercial operation. Fragmentation experiments were done at 
several sites and did not involve the application of leach solu- 
tions. Their objectives were to determine if sufficient 
permeability could be obtained for leaching. Fourteen pro- 
grams fall into the experimental category, with four of them 
involving the Bureau of Mines. Data tables are only included 
for those sites where leach solutions were applied. 

Bluebird Mine 

The Bluebird mine is owned by Ranchers Exploration and 
Development Corp. and is located in the Miami-Globe area 
of Arizona about 75 miles (120 km) east of Phoenix. Produc- 
tion from the open pit mine began in late 1964, and the oxide 
ore is heap leached. The host rock is the Pinal Schist. The 
grade of the deposit averages 0.5 pet (28) and the principal 
copper mineral is chrysocolla with minor amounts of azurite 
and malachite. In 1968, Ranchers built the first commercial 
SX-EW plant at the mine to process the pregnant heap leach 
solutions. Copper production in 1980 was 12.2 million lb (5.5 
X 10 6 kg). 

In 1979, a small-scale in situ leaching experiment was 
conducted in a section of the mine below the water table and 
under too much overburden to be considered for open pit 
mining. Vertical holes were drilled into the formation 100 ft 
(31 m) deep in a five-spot pattern with the corner holes spaced 
20 ft (6 m) apart. Steel casings, 2-in diam (51 -mm), were 
cemented in the four corner (injection) holes. The casings 
were perforated every 5 ft (1 .5 m) and then each well was 
hydrof raced. 



Ranchers officials have not publicly released any other 
information about the test except to say that the project has 
been "shelved" because it is not economic with current cop- 
per prices. 

Ranchers has considered leaching in place the 
remaining ore in the pit. The ore body still contains 65 million 
T (59 X 1 6 1) grading 0.53 pet Cu (28). This approach is being 
considered because it is no longer practical to remove the 
overburden required to mine the ore as an open pit. 

Cerrillos Deposit 

The Cerrillos deposit is located near Cerrillos, NM, about 
25 miles (40 km) south of Santa Fe, and is owned by Occiden- 
tal Minerals Corp. The deposit contains approximately 10 
million T (9 X 10 6 1) averaging 0.3 pet copper (0.2 pet acid 
soluble copper) and runs from the surface to 250 ft (76 m) 
in depth. The host rock is a granitic porphyry and chrysocolla 
is the principal copper mineral. 

Occidental wanted to develop an in situ mining system 
for small oxidized copper deposits above the water table. A 
100-ft (31 -m) cube of surface ore was prepared by detonating 
104,000 lb (47,200 kg) of AN-FO. Nine-in-diam (229-mm) 
blastholes spaced 13 ft (4 m) apart in a square pattern were 
used. The cube contained 80,000 T (72,600 1) of ore and had 
a surface area of 10,000 ft 2 (929 m 2 ). The prepared surface 
of the block is shown in figure 10. Seventy percent of the 
material was reduced to minus 4 in (102 mm) in size by the 
blast. 

A shaft was sunk to a depth of 120 ft (37 m) and a shot- 
creted drift was driven under the blasted ore. Five sets of 3-in- 
diam (76-mm) holes were fan drilled up into the blasted ore 
at 20-ft (6-m) intervals along the drift. These solution recovery 
holes varied in length from 25 to 58 ft (8 to 18 m) and were 
cased with 2-in-ID (51-mm) plastic pipe with 0.25-in (6-mm) 
perforations at 6-in (152-mm) intervals. No leaching was ever 
done, however, owing to changing environmental regulations 
which kept increasing costs. Occidental shut down the site 
in 1977 and is now in the process of selling it. 

The site was to have been leached at a flow rate of 0.045 
gpm/ft 2 (1 .83 Lpm/m 2 ) for a total flow of 450 gpm (1 ,700 Lpm) 
with pregnant solutions processed in a precipitation plant. 
The operation appeared technically feasible and a full-scale 
commercial operation had been planned. 

Consolidated Copper Co. Mine 

Consolidated Copper Co.'s Brooks ore body was located 
near Ely in east-central Nevada. Success by the Ohio Cop- 
per Co. in leaching its block caved workings prompted Con- 
solidated to do experimental leaching in a portion of its block 
caved workings in 1925 (6). The ore was in a shear zone in 
monzonite with a fairly well-defined footwall. Copper 
mineralization was basically sulfide with very little oxide pre- 
sent. The ore body was developed by drifts and raises and 
caved through finger chutes down to the 360-ft (126-m) level. 
The ore as mined assayed 1 .16 pet Cu, while the caved work- 
ings after mining were thought to contain about 0.3 pet Cu. 
The pregnant leach solution grade was about 1 .0 gpL Cu (4). 
Operating data are shown in table A-2. 

Emerald Isle Mine 

El Paso Mining and Milling Co. and the Bureau of Mines 
conducted a cooperative research program at the Emerald 
Isle open pit copper mine from 1973 to 1975. The objective 
of the program was to develop in situ mining methods for ore 
exposed in the pit bottom and also for ore under 200 ft (61 
m) of overburden adjacent to the pit. The mine is located in 
the northwestern portion of Arizona near the town of Kingman. 
Activities at the site included blasting and leaching 15,000 
T (1 3,600 1) of ore in the pit bottom, followed by the leaching 
of 100,000 T (90,700 t) of unblasted pit-bottom ore. A 



11 





Figure 10.— Prepared surface of blasted cube at Cerrlllos deposit. 



fragmentation experiment under 200 ft (61 m) of overburden 
was also done. Two blasts were detonated and the fragmen- 
tation was analyzed by core drilling and permeability testing 
(8). 

The host rock at the site is the Gila Conglomerate with 
an average thickness of 70 ft (21 m) and it dips 10° to 15° 
to the southwest. The principal copper mineral is chrysocolla 
with minor amounts of dioptase, tenorite, and cuprite. Dur- 
ing the life of the open pit, 1 .4 million T (1 .27 x 1 6 1) of ore 
averaging 1 .0 pet Cu was mined and the pit reached a depth 
of 200 ft (61 m). A cross section of the ore deposit showing 
the two test sites is shown in figure 11. The water table in 
the pit was maintained 5 ft (1 .5 m) below the pit floor. In the 
overburden test area, the water table was 235 ft (72 m) below 
the surface (8). 

A blast was detonated in the pit bottom to rubblize 15,000 
T (13,600 t) of ore for leaching. Seven 8.375-in-diam 
(213-mm), 50-ft (15-m) blastholes spaced 25 ft (8 m) apart in 
a seven-spot pattern were used. The holes had a powder col- 







BOO 



1,200 






Figure 11.— Crow section through Emerald Isle mine. 



umn averaging 22 ft (6.7 m), and 25 ft (7.6 m) of stemming. 
A total of 4,500 lb (2,043 kg) of slurry was detonated without 
delays. The powder factor was 0.3 Ib/T (0.15 kg/t). 
Topographic surveys before and after the blast revealed a 
maximum surface rise of 1.4 ft (0.43 m). The blast had a 
significant effect on fragmentation with core recovery, rock 
quality designation (ROD), average piece length, and longest 
piece all decreasing from preblast to postblast core. The RQD 
is obtained by measuring the total length of all pieces of core 
greater than or equal to 4 in (1 02 mm) and dividing the total 
by the distance drilled (36). 

Leaching of the blasted ore began in March 1974 and 
ran for 1 14 days. Dilute H 2 S0 4 leach solution was distributed 
on the surface through perforated pipes and recovered 
through a well on the east side of the blasted zone. Preg- 
nant leach solutions were processed in a precipitation plant. 
Total copper production during the test was 29,000 lb (13,150 
kg). Operating data are shown in table A-2. 

In December 1974, pit bottom leaching of about 100,000 
T (90,700 t) of unblasted ore began and continued for 190 
days. It was hoped that natural permeability would be suffi- 
cient for leaching. Seven recovery wells 50 ft (15 m) apart 
were used to collect the pregnant solutions. A total of 1 42,000 
lb (64,500 kg) of copper was produced during the test (8). 

Pit bottom leaching was stopped because the flow rates 
of leach solutions were not as high as desired, only 17 gpm 
(64 Lpm) per well. The highest production was from wells near 
the blasted portion of the pit. Flow rates per well ranged from 
5 to 45 gpm (19 to 170 Lpm). A drilling and blasting program 
to improve permeability was started but not finished because 
all operations at the mine were closed down. Operating data 
are shown in table A-2. 

Two test blasts were made through 200 ft (61 m) of over- 
burden at a site outside the open pit (fig. 1 1). The first blast 
had seven 9-in-diam (229-mm) holes averaging 272 ft (85 m) 
deep. A seven-spot pattern was used with 20-ft (6-m) hole 



12 



spacings. A second blast of three holes spaced 18 ft (5.5 m) 
apart was necessary because the first did not create enough 
permeability for adequate leaching. The explosive used in 
both blasts was a smokeless powder slurry. Powder factors 
were 0.95 Ib/T (0.48 kg/t) for the first blast and 1 .47 Ib/T (0.74 
kg/t) for the second (8). 

Both blasts had a significant effect on fragmentation, but 
permeability measurements were too low for adequate 
leaching. The two values measured after the second blast 
were 6 and 20 md. It is unknown whether these values were 
low because of insufficient blast-induced fracturing, or reseal- 
ing of fractures. Another factor may have been the bentonite 
drill mud (used to drill the blast and core holes) which forms 
a low permeability wallcake on the borehole. 

The Emerald Isle Mine was recently purchased by TRC 
Enterprises, Inc. Initial plans are to leach the pit bottom ore 
in situ when copper economics improve. 

Johnson Mine 

The Bureau of Mines and Cyprus Mines Corp. conducted 
a cooperative research program to investigate the in situ min- 
ing potential along the fringes of the open pit Johnson mine 
17 miles (27 km) west of Willcox, AZ. This program led to 
a test blast detonated in August 1977, for evaluating blast 
design, solution flow rate, and solution containment (7). No 
in situ mining was done at the site. 

The Johnson mine is an oxide copper deposit mined by 
open pit-heap leach methods. Pregnant leach solutions are 
processed in a SX-EW plant. The metashale ore is in the lower 
member of the Abrigo Formation and is underlain by 150 ft 
(46 m) of impervious Bolsa Quartzite. The principal copper 
mineral is chrysocolla with minor amounts of azurite and 
malachite. The grade of the deposit averages about 0.5 pet 
acid soluble copper. The ore has very low tensile strength 
[24 psi (172 kPa)], a porosity of 11 pet, and permeability of 
1.7 md as measured on core samples. Field permeability 
ranges from 5 to 50 md (7). 

A cross section through the mine is shown in figure 12. 
The pit at the time of the test and the proposed final pit limits 
are shown. The test blast area was 56 ft (17 m) below the 
surface and extended 185 to 224 ft (56 to 68 m) deep. Figure 
13 shows the test blast design. Thirteen 9.875-in-diam 
(250-mm) blastholes were spaced 14 ft (4.3 m) apart in an 
equilateral triangle pattern. The pattern was elongated in the 
down-dip direction with the deepest holes on the northeast 
end. A total of 51,500 lb (23,380 kg) of AN-FO was loaded 
into the 13 blastholes. A constant stemming height of 56 ft 
(17 m) was maintained. The blast was bottom primed with 
two 0.4-lb (0.18-kg) cast primers. A powder factor of 2.2 Ib/T 
(1.1 kg/t) fractured about 19,700 T (17,870 t) of ore assum- 
ing a 4-ft (1 .2-m) overbreak. These figures are based on ore 
in the powder column only and not ore in the stemming 

-Present pil 






Figure 12.— Cross section of Johnson mine deposit. 



KEY 
O Blastholes 
y^ 18 msec delays 
A Preshol permeability hole 
O Postshot pefmeobility hole 

Figure 13.— Johnson mine test blast design. 

region. The powder factor was higher than normally used in 
bench blasting but was considered necessary to break ore 
in a confined situation. 

Topographic surveys were run before and after blasting. 
The surface rose over a broad area with significant displace- 
ment along a north-south-trending fault. The volume increase 
at the surface was 1 ,500 yd 3 (1 ,150m 3 ). The postshot drill core 
was very highly fractured with only 23 pet recovery and an 
RQD of 2 pet compared with 87 pet recovery and 51 pet RQD 
for preshot core (7). 

Constant-head permeability tests were run before and 
after blasting. The test holes are shown in figure 13. Preshot 
permeabilities ranged from 15 to 43 md, while postshot values 
ranged from 180 to 8,500 md. These postshot values are con- 
sidered adequate for successful leaching. 

A water circulation test was run by injecting water into 
holes IH-1 and IH-2 and by monitoring the water in IH-3 (fig. 
13). During this test 300,000 gal (1 .4 X 10 6 L) of water were 
injected at 35 gpm (132 Lpm) in an attempt to fill the bottom 
of the fractured zone. However, very little water was observed 
in the 224-ft-deep (68-m) IH-3 hole. The water may have 
escaped from the fractured zone along the Bolsa Quartzite 
contact, or the IH-3 hole may not have been deep enough 
and insufficient water was injected to fill all the void spaces 
created at the bottom of the fracture zone. Based on this test, 
it was determined that a solution containment system, such 
as grouting, would be necessary for successful leaching. 

Kimbley Pit 

The Kimbley pit is located in east-central Nevada, near 
the town of Ruth, and is part of Kennecott Copper Corp.'s 
Nevada Mines Division. It is one of several small open pits 
in the area and has been worked to its economic limit. The 
host rock has been tentatively identified as a limey sediment 
which has been intruded by biotite-argillic porphyry (35). The 
principal copper mineral is chalcocite and the ore contains 
significant amounts of pyrite. 

Two preliminary permeability tests and a pilot scale in 
situ leach mining test were done at the site. The objectives 
of the preliminary tests were the determination of formation 
permeability and extraction of copper solutions from the for- 
mation (35). 

The first test was conducted in 1968 on a bench 250 ft 
(76 m) above the pit bottom. Five injection holes were drilled. 
They were 9-in diam (229-mm), 40 ft (12 m) deep, 50 ft (15 
m) apart, and 25 ft (8 m) from the edge of the bench. Acidified 
water was pumped into the holes for 2 weeks. The holes were 
kept full of solution, but not injected under pressure. The 
average permeability at the start of the test was 38.4 md, but 
by the end of the test it had risen to 268.8 md. Subsequent 
tunneling and blasting revealed that solutions radiated from 



13 



the holes in a cone shape that reached 40 ft (12 m) in diameter 
at a depth of 165 ft (50 m) below the top of the hole (35). 

The second test was done at a site 1 ,000 ft (305 m) east 
of the pit. A series of 100-ft (31 -m) vertical injection holes were 
drilled from the surface above an old exploration drift. Leach 
solution injection into the holes produced a cone of influence 
160 ft (49 m) in diameter. Permeability averaged 6,209 md. 
The drift intercepted about 7 pet of the injected solution (35). 

The pilot leaching test was conducted in the exploration 
drift used for a second test. A recovery well was drilled from 
the surface 265 ft (81 m) deep into a bowl-like limestone for- 
mation underlying the ore. The drift was modified to facilitate 
leach solution application. Dams were built to contain the 
solution in a portion of the drift, and holes were drilled for 
solution distribution to supplement the natural fracture 
system. Beginning in January 1970, acidified fresh water was 
pumped between the dams in the drift at the rate of 50 gpm 
(190 Lpm). The solution was allowed to percolate down 
through the natural fractures in the ore, and migrate to the 
recovery well in the limestone basin to be pumped to the 
surface. 

Injection was continued for 17 months. Only about 0.2 
gpm (0.8 Lpm) of solution was migrating to the well with an 
average grade of 0.15 gpL Cu. Both solution flow and grade 
were uneconomic and the test was discontinued. Experimen- 
tation at the site continued through 1972, however, with ef- 
forts involving hydraulic fracturing, liquid oxygen injection, 
and acidified ferric sulfate leach solution. The results of these 
tests have not been published. Operating data are shown in 
table A-2. 

Lakeshore Mine 

The Lakeshore mine is located 30 mi (48 km) southwest 
of Casa Grande. AZ. The property contains three copper bear- 
ing bodies: two sulfide and one oxide. Hecla Mining Co. in- 
itially developed the property (25) in the late 1960's as a block 
caving operation in both sulfide and oxide ore. The mine was 
sold to Noranda Lakeshore Mines, Inc., in 1979 after the cop- 
per recession of the mid-1 970's forced Hecla to abandon the 
project (26). Noranda continued with conventional 
underground mining and vat leaching of the oxide ore, and 
opened a new SX-EW plant in 1981 to process the pregnant 
vat leach solutions. 

Low copper prices are again causing a planned shut- 
down of underground mining for late 1983. At that time a com- 
plete changeover to in situ mining is scheduled to have taken 
place. This will be cheaper, require fewer people, and take 
advantage of equipment already at the site (26). 

Experimental work for the in situ mining began in early 
1983. Leaching is being done in block caved areas. Dilute 
sulfuric acid leach solution is applied to the ore through in- 
jection holes from the surface. They have been drilled in the 
subsidence area that resulted from the caving operation, 
average 550 ft (168 m) in depth, and are cased. Five dams 
buift in the underground workings are used to collect the preg- 
nant leach solution. From there it is pumped to the SX-EW 
plant on the surface. Detailed operating data are not yet 
available. 

Medler Mine 

Perhaps the first attempt at in situ copper mining took 
place between 1906 and about 1909 at the Medler mine near 
Clifton, AZ (2). The ore was the primary sulfide portion of a 
porphyry copper deposit. It had an average grade of 0.38 pet 
Cu which was considered at the time to be too low for con- 
ventional mining. 

At the time the mine was leased for this experimental 
work, it consisted of two adits vertically separated by 60 ft 
(18 m) with a connecting winze. Development work for 
leaching consisted of driving another adit 1 00 ft (30 m) above 
the upper level and sinking the winze 100 ft (30 m) to get 



below the water table. At the bottom of the winze, another 
level was projected to facilitate collection of the drainage 
water (2). Drifts were driven off the main adits on all levels 
at intervals no greater than 200 ft (61 m) for water applica- 
tion and recovery. 

Leaching was done by flooding the second level with 
mine water and allowing it to seep down to the third level 
where it was collected and passed through cementation 
launders. The launders were located in the third level adit. 
Makeup water was bailed from the fourth level. 

Initial water seepage was very slow. It took months for 
any water to show up on the third level which was only 60 
ft (18 m) below the second. Once the rock was saturated, 
however, the flow rate increased. Pregnant leach solution 
grades ranged from 0.2 to 0.6 gpL. The first carload of cop- 
per precipitate was shipped in July 1908, 2 yr after develop- 
ment work was begun (2). The operation was closed by the 
right of eminent domain when a railroad tunnel was driven 
through the mine. 

Mountain City Mine 

The Mountain City mine is located about 7 miles (1 1 km) 
southwest of Mountain City, NV. It was first operated by the 
Anaconda Copper Co., as the Rio Tinto mine, from 1932 to 
1948 with copper ore averaging 9.75 pet being mined by 
square set stoping methods. The mosjt recent in situ copper 
leaching activities took place from 1972 to 1974 when the 
property was co-owned by Cliffs Copper Corp., a subsidiary 
of Cleveland-Cliffs Iron Co. and E.I. du Pont de Nemours & 
Co. (4). 

The ore occurs in a stratigraphically restricted zone of 
black and gray phyllite with associated quartzite lenses in a 
shale sequence called the Valmy formation. The major cop- 
per mineralization is supergene chalcocite which was 
deposited near the water table, 200 ft (61 m) below the sur- 
face. Minor copper minerals are chalcopyrite, cuprite, 
malachite, chrysocolla, azurite, and native copper. The 
mineralization was entirely along fracture planes and as 
replacement or coatings on disseminated pyrite. 

Copper was recovered from the Rio Tinto mine from 
August 1966 through February 1970 through a leaching pro- 
cess in which solution was withdrawn from the flooded mine, 
passed over scrap iron to precipitate the copper values, 
acidified with sulfuric acid to about pH 2, and returned to the 
mine (6). 

Initial operations distributed barren leach liquor to four 
holes that entered the mine at the 222-ft (68-m) level. Some 
leach liquor was also added to four subsidence pits above 
the ore body. Three additional holes entering the 300-ft (92-m) 
level were drilled and activated in early 1969. Approximately 
one-third of the barren liquor was returned directly to the mine 
shaft because of the limited capacity of the water injection 
holes. 

Compressed air [80 to 100 psi (551 to 689 kPa)] was fed 
through two holes entering the 400-ft (1 22-m) level of the mine 
(about 150 to 200 ft (46 to 61 m) below the water surface) 
during 1968 to 1969 to assist oxidation and the leaching pro- 
cess (6). 

During summer and fall months, copper was also leached 
from a nearby tailings pond. Pregnant liquor from the tailings 
operation was combined with pregnant liquor from the mine 
ahead of the cementation plant. During these periods, the 
amount of copper in the plant effluent solution increased as 
the loading on the cementation plant increased. Pregnant 
liquor grade from the mine usually increased an equivalent 
amount because the effluent was recirculated (6). 

Operations were suspended in February 1 970 when the 
supply of tailings had been exhausted and the grade of preg- 
nant liquor from the mine was too low to support further 
operations. 

Preparations for in situ leaching began again in 1972 
when dewatering of the old workings began. This was fol- 



14 



lowed by shaft rehabilitation. The plan was to develop an un- 
mined portion of footwall ore, known as the South Ore Body, 
by block caving, and then leach the caved areas. This method 
was determined to be the only economic way to recovering 
copper from the site. 

Two test blocks were developed and caved. The first, 
140 by 150 by 200 ft high (43 by 46 by 61 m) contained 
306,000 T (277,600 1) and averaged 1.1 pet Cu. The second 
block contained 487,000 T (441 ,800 1) and averaged 0.93 pet 
Cu. Development work was done at the 400-ft (122-m) level. 
The caving procedure was based on normal long-hole drill- 
ing and block-caving methods. A draw of 12.5 pet was tried 
on the first block, but this caused undesirable caving above 
the 200-ft (61 -m) level. The draw on the second block was 
decreased to 6 pet, which was estimated to be the minimum 
amount necessary to induce the desired degree of caving. 
Draw material was placed in heaps on the surface and 
leached (4). 

The leach solution was a combination of H 2 S0 4 and 
recycled mine water, which had been routed through a tail- 
ings area to become enriched in ferric sulfate. Solutions were 
introduced to the caved blocks through injection wells from 
the surface. They were initially drilled on 50-ft (15-m) centers; 
however, collapsed casings and low injection rates required 
drilling on 25-ft (8-m) centers. The injection rate was initially 
25 gpm (95 Lpm) per hole which declined in 1 to 2 months 
to to 5 gpm (0 to 19 Lpm) because of casing collapse and 
silt buildup. This resulted in gross variations in the total flow 

(4). 

Solutions percolated down through the caved ore to the 
400-ft (122-m) level, and collected with mine seepage at the 
450-ft (137-m) level. Solutions were pumped to the precipita- 
tion plant with a submersible pump. 

Leach solution was first applied to the first block in March 
of 1974 and the second block in May 1974. After solving in- 
itial startup problems, the blocks were continuously leached 
from June through November 1974. The pregnant leach solu- 
tion at the 400-ft (1 22-m) level graded 1 .5 to 2.0 gpL Cu, but 
after dilution with mine seepage the grade to the precipita- 
tion plant was 0.5 to 0.6 gpL. During the 6 months of con- 
tinuous operation, a total of 850,000 lb (385,900 kg) of cop- 
per was produced from the two blocks, about a 5.5-pct 
recovery (4). 

In December 1974 all activities at the mine were ter- 
minated because of higher than expected development costs 
and low copper prices [$0.55/lb ($1 .21 /kg)]. There were also 
unresolved technical problems with solution distribution and 
aeration which resulted in a slower than anticipated leaching 
rate for the copper sulfide minerals. The mine was sold to 
another company, which in turn, sold it again. Operating data 
are shown in the table A-2. 

Nacimiento 
Mine 

The Nacimiento mine is located about 4 miles (6.4 km) 
southeast of Cuba, in north-central New Mexico. In 1971, 
Earth Resources Co. began an open pit mining operation at 
the site which continued 3.5 yr. The deposit had estimated 
reserves of 9.6 million T (8.7 X 10 6 1) of ore averaging 0.66 
pet Cu. Mine production totaled 2.5 million T (2.3 x 10 6 1) with 
a cutoff grade of 0.3 pet. The mine closed because of low 
copper prices and slope stability problems. 

The host rock is the Agua Zarca Sandstone, which is 1 20 
ft (37 m) thick and is overlain by shale and underlain by 
mudstone. Both of these confining layers are impervious. 
Permeability of the sandstone ranges from 300 to 3,000 md, 
which is sufficient for in situ leaching without blasting. The 
formations dip 29° to 34° to the southwest, and the principal 
copper mineral is chalcocite. All of the ore considered for 
leaching is below the water table which is at the bottom of 
the open pit. Column leaching tests on ore samples showed 
that ferric sulfate leach solution yielded excellent recovery, 



P-5 




LEGEND 



a Test well 

O Abandoned dewatering we 



Scale, ft 
Figure 14.— Nacimiento mine well location map. 



although oxygen may have to be added for leaching below 
the water table. 

Hydrology tests were run in 1978. The test site was 
located on a bench in the southwest side of the pit. Four wells 
were drilled in a square pattern as shown in figure 14. The 
wells were 100 to 1 10 ft (30 to 40 m) deep and were cased 
with 4-in-diam (102-mm) plastic pipe; the sandstone ore layer 
was screened through at least 80 pet of its thickness. An 
abandoned dewatering well was also used. Drawdown and 
recovery tests were run, with pumping done from well P-4 
and water levels monitored at all wells (39). The test results 
were "positive," proving a favorable hydrology for in situ 
leaching, but no further development has taken place 
because of low copper prices. Earth Resources still controls 
and maintains the property and plans to continue with the 
program when copper economics improve. 

Safford Deposit 

The Safford deposit is located 9 miles (14 km) north of 
the town of Safford, AZ, which is about 80 miles (130 km) 
northeast of Tucson. The host rocks for the deposit are 
andesitic volcanics. Principal copper minerals are chrysocolla, 
chalcopyrite, brochantite, chalcocite, and covellite with minor 
amounts of bornite. The deposit contains approximately 2 
billion T (1.8 X 10 9 1) averaging 0.41 pet Cu, about half of 
which is relatively enriched oxide ore. The deposit is up to 
4,000 ft (1 ,220 m) long and about 1 ,600 ft (488 m) thick and 
is overlain by 500 to 1 ,300 ft (150 to 400 m) of leached cap- 
ping and barren volcanics (10). It is above any known water 
table. 

Kennecott Minerals Co. purchased the property in 1959 
after 4 yr of exploration. In the mid-1 960's it proposed Pro- 
ject Sloop, which was to have been a joint effort with the 



15 



Atomic Energy Commission to fragment a portion of the ore 
body with a nuclear explosive for in situ mining (10). In the 
early 1970's Project Sloop was canceled because of per- 
ceived environmental restrictions. 

Research was then redirected to conventional means for 
fragmenting the ore. The goal was to develop a system for 
in situ leaching the sulfide ore in the deposit. The research 
effort covered many areas including mineralogy, petrology, 
leaching chemistry, laboratory leaching, permeability testing, 
geophysical logging, ground water tracers, directional drill- 
ing, blasting, five-spot pattern leaching, plant design and 
economic analysis. It was one of the most intensive and ex- 
pensive research programs to date, and the results are pro- 
prietary. However, several patents concerning various 
aspects of deep in situ mining were granted (9, 14-16). 

Currently there is no research being conducted at Saf- 
ford because of disappointing test results and the low price 
of copper. However, Kennecott plans to continue research 
in the future. 

Seneca Mine 

The Bureau, in cooperation with Homestake Copper Co., 
performed a confined blasting test in an underground native 
copper mine in the Keweenaw Peninsula of upper Michigan. 
It was done to determine the feasibility of using such blasting 
(with no relief for expansion) to fragment deep ore bodies for 
leaching (5). The test was done in 1976 in the abandoned 
underground workings of the Seneca mine near Mohawk, Ml. 

The geology of the district is a series of basaltic flows, 
often interspersed with conglomerate beds, which were tilted 
subsequent to their extrusion and now dip toward Lake 
Superior. In the mine, the copper occurred in the 
amygdaloidal top of the Kearsarge Basalt, which dips about 
37 c at the mine. 

The basic approach to confined blasting was to drill 
blastholes downdip into the formation from the third level drift, 
280 ft (85 m) below the surface. Parameters such as hole 
depth, hole diameter, hole spacing, explosive type, and stem- 
ming were considered in designing a blast that would break 
rock without moving it. Hole deptn was set at 40 ft (12 m) 
to minimize the effects of the drift on the blast yet keep drilling 
costs within the research budget. A 3-in-diam (76-mm) hole 
was then selected based on the expected range of burdens 
associated with the 10-ft (3-m) ore zone thickness. Finally, 
a slurry blasting agent suitable for wet conditions was chosen 
for the shots with a 20-ft (6-m) powder column and 20 ft (6 
m) of water stemming (5). 

The only significant blasting parameter remaining for 
evaluation in the tests was blasthole spacing, which held the 
key to economic feasibility. If the blastholes had to be drilled 
very close together to create adequate permeability, confined 
blasting would be uneconomical. To evaluate fracturing and 
permeability as a function of blasthole spacing, a blast 
incorporating three different triangular patterns was designed 
(fig. 15). 



+ Co* »e«« (eodMOfi) 



The three burden to blasthole diameter ratios selected 
for the test series were 10, 14, and 18. These ratios cor- 
responded to blasthole spacings of 2.5, 3.5, and 4.5 ft (0.76, 
1 .07, and 1 .39 m). The calculated powder factors in the ore 
around the loaded portions of the blastholes were 8, 4, and 
2.5 Ib/T (4, 2, and 1 .2 kg/t) respectively (5). Core obtained 
from these holes was analyzed for fractures; permeability 
tests were also conducted in the blastholes before shooting. 

The fragmentation effectiveness was evaluated with 
postshot core holes drilled in the center of each triangular 
pattern. Fracturing in the core was then compared with that 
from the preshot core; formation permeability was also 
compared. 

All preshot tests and analyses pointed to a "tight" 
impermeable formation that contained few fractures. Crude 
measurements of permeability ranged from to 1.5 md. 
Blasting did create new fractures, particularly at the closer 
spacings with their associated high powder factors, but the 
permeability changes created by the fracturing were small. 
Even with injection pressures of 80 psi (552 kPa) very little 
fluid was transmitted from one hole to the next. Because the 
best permeability achieved with the close spacings was only 
40 md, confined blasting simply did not create enough 
permeability to consider leaching. 

Sierrita Mine 

The Bureau of Mines performed 'a fragmentation experi- 
ment at the Duval Corp. Sierrita open pit copper-molybdenum 
mine in 1973. The mine is about 24 miles (39 km) south of 
Tucson, AZ, in Pima County. The experiment consisted of 
a preblast evaluation of the site, drilling and blasting, and 
postblast evaluation. No leaching was done at the site (36). 

The dominant rock type was well-weathered quartz mon- 
zonite porphyry that had considerable jointing and faulting. 
Assays of samples taken during blasthole drilling averaged 
0.14 pet Cu, with 0.13 pet acid soluble. 

Preblast evaluation was done by diamond core drilling 
three NX size [approximately 3-in-diam (76-mm)] holes in the 
middle of the 15-, 20-, and 25-ft (4.6-, 6.1-, and 7.6-m) 
blasthole spacing areas as shown in figure 16. The 10 
blasthole locations and blast delay sequence are also shown 
in this figure. The 9-in-diam (229-mm) blastholes were 110 
ft (33.5 m) deep. Each hole had a powder column of 50 ft 
(15 m) and 60 ft (18 m) of stemming. The blast contained a 
total of 17,440 lb (7,918 kg) of 10 pet aluminized slurry blasting 
agent. Powder factors, assuming infinite patterns, were 0.40, 
0.63, and 1 .1 3 Ib/T (0.20, 0.32, and 0.57 kg/t) for the 25-, 20-, 
and 15-ft (7.6-, 6.1-, and 4. 6-m) patterns, respectively (36). 

Postblast studies included a topographic survey, map- 
ping of surface fractures, fragment size distribution 




- 



Scole " 



KEY 

Biosthole 
D'omond drill holes 
l,2,ond 3 preshot 
4,5,6,7,8, one) 9 postshot 
9-ms delays 



Figure 15— Senses mine blasthole pattern in drift wall. 



Figure 16.— Sierrita mine test blast design. 



16 



Table 2.— Slerrlta mine drill core data 







Length 


Weight 


ROD, 


Largest 


Average size 


Location 


Hole 


recovery, 


recovery, 


pet 


piece, 


of pieces >1 in, 






pet 


lb/ft 




in 


in 


Preshot 


1 


101 


2.63 


37 


13 


3.1 


Do 


2 


98 


2.58 


35 


17 


3.2 


Do 


3 


96 


2.58 


37 


12 


3.2 


25-ft pattern 


4 


81 


2.08 


28 


10 


2.8 


Do 


7 


76 


1.90 


19 


11 


2.8 


25-ft pattern 














(off center) . 


9 


62 


1.61 


19 


12 


2.7 


20-ft pattern 


5 


53 


1.20 


9 


8 


2.2 


Do 


6 


51 


1.20 


12 


9 


2.5 


15-ft pattern . 


8 


37 


.99 


10 


9 


2.3 



measurements of surface material, and six NX core holes 
located as shown in figure 16. Laboratory measurements 
done on preblast and postblast cores were recovery by length 
and weight, RQD, and fragment size distribution. 

The surface rise over the blast averaged about 5 ft (1 .5 
m), and the total volume increase produced by the blast was 
5,100 yd 3 (3,900 m 3 ). Table 2 lists the location, length core 
recovery, weight core recovery, RQD, largest piece, and 
average size of pieces greater than 1 in (25 mm) for nine 
diamond-drill core holes. Length core recovery and weight 
core recovery were measured after the core was returned to 
the laboratory. The length core recoveries measured in the 
core boxes were higher (101 pet for hole 1) than would have 
been obtained from measurements taken before the core was 
removed from the core barrel. Although there is a good cor- 
relation between length and weight recovery, the weight core 
recovery was considered the most accurate method for 
evaluating blast damage. The average size of core pieces 
1 in (25 mm) or greater was determined by dividing the total 
length of all pieces greater than 1 in (25 mm) by the number 
of pieces greater than 1 in (25 mm). 

The drill core data show that better breakage occurs as 
blasthole spacing decreases, and fragmentation improves as 
distance from the center of the equilateral triangle patterns 
increases (see hole 9 in table 2). Factors other than fragmen- 
tation affect copper recovery, and actual leaching would have 
been desirable. However, the fragmentation analysis in- 
dicates that all three blast patterns produced adequate 
breakage for in situ mining. 

Van Dyke Deposit 

The Van Dyke deposit partially underlies the town of 
Miami, AZ, which is about 75 miles (120 km) east of Phoenix. 



The deposit contains approximately 100 million T (90 X 10 6 1) 
of ore with an average grade of 0.5 pet Cu. It dips about 15° 
and ranges from 1,100 to 2,000 ft (335 to 610 m) deep 
beneath the town and is overlain by the Gila Conglomerate 
(27). Copper mineralization occurs in hairline fractures in the 
Pinal Schist (22). The major copper mineral is chrysocolla 
with minor amounts of azurite and malachite. 

Occidental Minerals Corp. purchased the lease for the 
property in 1968 and spent $11 million on exploration and 
tests between then and 1980 (27), when it developed a plan 
for mining the ore body in situ. Conventional mining methods 
were not considered viable because of deposit depth, loca- 
tion, and grade. 

Two in situ mining tests were conducted below the water 
table with injection and recovery wells drilled from the sur- 
face. The first test, in 1976, involved two wells 75 ft (23 m) 
apart and just over 1 ,000 ft (305 m) deep (22). The 10-in-diam 
(254-mm) holes were drilled and cased with 4-in-diam 
(102-mm) fiberglass casing. Both wells were then hydro- 
fraced. This fracture was supposed to extend a maximum of 
200 ft (61 m) from the wells. After the casings were pressure 
tested for leaks, dilute H 2 S0 4 leach solution was injected into 
one well, and production of solution from the other well began. 
Injection and production were done at the same rate. Preg- 
nant leach solutions produced during the test were 
transported to a nearby SX-EW plant for processing. 

A second leach test was then conducted using a five- 
spot pattern with 100-ft (31 -m) well spacings. Five 10-in-diam 
(254-mm) holes were drilled and cased with 4-in (102-mm) 
fiberglass casing. The test zone was between 1 ,000 and 1 ,200 
ft (305 and 366 m) deep. All of the wells were hydrofraced. 
Dilute H 2 S0 4 solution was injected in the center well and preg- 
nant solutions were produced from the corners. The test ran 
for several months and was considered successful. Details 
of the testing are proprietary. 

At this point, Occidental applied for two special-use per- 
mits from the town of Miami to do further testing in another 
portion of the ore body, but the permits were denied. After 
a long and costly legal battle over the permits, Occidental 
dropped its lease on the property in October 1980 (24). There 
is currently no activity at the site. 

The full-scale commercial operation planned by Occiden- 
tal would have involved a shaft outside of town, and a grid- 
work of nearly horizontal drifts above the ore body. Injection 
and production wells would have been drilled from the drifts. 
A SX-EW plant was also planned. The operation would have 
employed about 200 people and had an estimated life of 15 
yr (22). Operating data for the leaching tests are shown in 
table A-2. 



SUMMARY 



To date, there have been at least 24 sites in the United 
States where in situ copper mining production or research 
has taken place. Three have been commercial operations with 
ore body preparation (blasting), seven have been commercial 
operations in old mine workings, and 14 were experimental 
sites. Of these experimental sites, only eight reached the 
leach-solution application stage. 

Ore bodies that are too low grade or small to be mined 
by conventional methods have potential for in situ mining 
because of the relatively low capital and production costs 
involved. The method is not normally considered for other 
deposits because of its relatively low recovery. Leaching of 
old mine workings such as block caves, backfilled stopes, 
and open pits, is often an economic method for recovering 
additional copper when conventionally minable reserves have 
been depleted. Experimental work has typically been done 
on a small scale to determine the feasibility of commercial 
operations, however, several of the Bureau of Mines 
experiments were directed specifically at ore fragmentation 
by blasting and were not leached. 



At present the only two active, commercial, in situ cop- 
per operations in the United States (Copper Queen Branch 
and Miami mine) involve leaching of old mine workings. The 
Lakeshore mine is the only active experimental site, and 
Noranda is planning to go commercial in the near future. 

In situ copper mining activities have been shut down for 
several reasons, with the most common one being economic 
(low copper prices, excessive ore preparation costs, etc.). 
Other causes of shutdowns have been expansion of open pit 
operations into leach areas, environmental concerns, 
technical difficulties (inability to contain solutions, low preg- 
nant solution grade, etc.), and one operation was closed when 
the lease agreement was not renewed. 

Many of the companies plan to resume leaching pro- 
grams when copper economics improve, and Ranchers is 
considering a plan to blast and leach in situ, the remaining 
ore in the Bluebird open pit. In situ mining will become much 
more attractive and play an increasingly important role in 
future copper production as conventional mining costs 
increase and ore grades decrease. 



17 



REFERENCES 



1. Anderson. A. E.. and F. K. Cameron. Recovery of Copper by 
Leaching, Ohio Copper Co. of Utah. Trans. AIME, v. 73, 1926, pp. 
31-57. 

2. Austin, W. L. Leaching of Copper From Rock in Place. Mines 
and Methods, v.2. No. 7. March 1911, pp. 153-156; No. 8, April 1911, 
pp. 187-191. 

3. Bhappu. R. B. In Situ Extraction and Leaching Technology. Pres. 
at Inter-Regional Seminar on the Economics ofMineral Engineer- 
ing, Ankara, Turkey. Apr. 5-16, 1976. 39 pp; available for consulta- 
tion at BuMines Twin Cities Research Center, Minneapolis, MN. 

4. Catanach, C. B. Development and In-Place Leaching of Moun- 
tain City Chalcocite Ore Body. Proc. Int. Symp. on Copper Extrac- 
tion and Refining, Met. Soc., AIME, Las Vegas, Nev., 22-26, 1976 
(pub. as Extractive Metallurgy of Copper— Hydrometallurgy and Elec- 
trowinning, ed. by J. C. Yannopoulos and J. C. Agarwal). Port City 
Press. Baltimore, MD.. v. II. 1976, pp. 849-872. 

5. Chamberlain, P. G. In-Place Leaching Research at the Seneca 
Mine. Mohawk, Mich. Pres. at Ann. Spring Technical Meeting of Up- 
per Peninsula Section. AIME. Ml Tech. Univ., Houghton, Ml, Apr. 
21, 1977, 14 pp.; available for consultation at BuMines Twin Cities 
Research Center, Minneapolis, MN. 

6. Chase, C. K., E. A. Nordhousen, R. B. Bhappu, J. B. Fletcher, 
J. V. Rouse, and W. D. Gould. Feasibility of In Situ Leaching of 
Depleted Underground Copper and Uranium Mines. Mountain States 
Research and Development, Inc., Final Rept.. BuMines Contract 
J0295045. January 1982, in two volumes, v. 1, 115 pp., v. 2, 81 pp; 
available for consultation at BuMines Twin Cities Research Center, 
Minneapolis, MN. 

7. D'Andrea, D. V., P. G. Chamberlain, and J. K. Ahlness. A Test 
Blast for In Situ Copper Leaching. Pres. at 1 978 AIME Ann. Meeting, 
Denver, CO, Feb. 26-Mar. 2, 1978, Preprint 78-AS-112, 15 pp. 

8. D'Andrea. D. V., W. C. Larson, L. R. Fletcher, P. G. Chamberlain, 
and W. H. Engelmann. In Situ Leaching Research in a Copper 
Deposit at the Emerald Isle Mine. BuMines Rl 8236, 1977, 43 pp. 

9. Davidson. D. H.. and R. V. Huff (assigned to Kennecott Copper 
Corp.). Well Stimulation for Solution Mining. U.S. Pat. 3,917,345, 
Nov. 4, 1975. 

10. Engineering and Mining Journal. Kennecott Sets Sights on 
Nuclear Test for In Situ Recovery of Copper. V. 168, No. 11, 
November 1967, pp. 116-122. 

11. . Ranchers Big Blast Shatters Copper Orebody for In- 

Situ Leaching. V. 173, No. 4, April 1972, pp. 98-100. 

12. Fletcher, J. B. In Place Leaching. Skillings Min. Rev., v. 63, 
No. 17. Apr. 27, 1974, pp. 7-10. 

13. . In Place Leaching at Miami Mine, Miami, Arizona. 

Pres. at AIME Centennial Ann. Meet., Soc. Min. Eng., AIME, New 
York, March 1971. AIME Preprint 71-AS-40; Trans. Soc. Min. Eng., 
AIME. v. 250, No. 4, December 1971, pp. 310-314. 

14. Hsueh, L, R. A. Hard, D. H. Davidson, and R. V. Huff (assigned 
to Kennecott Copper Corp.). In-Situ Mining Method and Apparatus. 
U.S. Pat. 4,116.488. Sept. 26, 1978. 

15. Huff, R. V.. and D. H. Davidson (assigned to Kennecott Cop- 
per Corp.). Method for In Situ Minefields. U.S. Pat. 4,125, 289, Nov. 
14, 1978. 

16. Huff, R. V., and D. J. Moynihan (assigned to Kennecott Cop- 
per Corp.). Lixiviant Recirculator for In Situ Mining. U.S. Pat. 
4,079.998. Mar. 21, 1978. 

17. Hunkin, G. G. A Review of In Situ Leaching. Pres. at AIME 
Ann. Meeting, Soc. Min. Eng., AIME, New York, Feb. 26-Mar. 4, 1971 , 
AIME Preprint 71-AS-88, 23 pp. 



1 8. Longwell, R. L. In Place Leaching of a Mixed Copper Ore Body. 
Proc. Solution Mining Symp., AIME Ann. Meeting, Dallas, TX, Feb. 
25-27, 1974, pp. 233-242. 

19. Malouf, E. E. Copper Leaching Practices. Pres. at Ann. 
Meeting, Soc. Min. Eng., AIME, San Francisco, CA, Feb. 20-24, 1972, 
AIME Preprint 72-AS-84, 7 pp. 

20. Mining Record (Denver, CO). Miners Angered by Abandon- 
ment of Berkeley. V. 94, No. 22, June 2, 1982, p. 5. 

21 . Murr, L. E. Theory and Practice of Copper Sulphide Leaching 
in Dumps and In-Situ. Miner. Sci. Eng., v. 12, No. 3, July 1980, pp. 
121-189. 

22. Occidental Minerals Corp. The Oxymin Project at Miami, 
Arizona. A Summary of a Presentation Made to Miami, Arizona Town 
Council, Sept. 12, 1977, 5 pp.; available for consultation at BuMines 
Twin Cities Research Center, Minneapolis, MN. 

23. Pay Dirt, Arizona Edition (Bisbee, AZ). Cities Service Puts Cop- 
per Properties on the Auction Block. No. 504, June 1981, pp. 1,6-8. 

24. . Delays Lead Occidental Minerals to Kill Miami 

Leaching Plan. No. 496, October 1980, pp. 1, 12. 

25. Noranda Converting Copper Operation to In Situ 

Leaching. No. 522, December 1982, pp. 5-6. 

26. Noranda Lakeshore Switch to In Situ Leaching 

Nearly Complete. No. 523, January 1983, pp. 1, 5-7. 

27. . Oxymin Plans Final In Situ Copper Leaching Tests 

at Miami. No. 486, December 1979, pp. 1, 4. 

28. . Ranchers Rapidly Becoming a Major Precious Metals 

Producer. No. 509, November 1981, pp. 26, 28, 30. 

29. Pay Dirt, Supplement to Arizona Edition (Bisbee, AZ). Phelps 
Dodge— A Copper Centennial, 1881-1981. Summer 1981, pp. 14-18. 

30. . Phelps Dodge— A Copper Centennial, 1881-1981. 

Summer 1981, p. 74. 

31. Prescott Newspaper (Prescott, AZ). Kirkland Blast Will Open 
New Body of Copper. Apr. 18, 1973, p. 1. 

32. Rudershausen, C. G. Copper Solution Mining at Old Reliable. 
Pres. at National Meeting of American Inst, of Chem. Eng., Salt Lake 
City, UT, August 18-21. 1974, 11 pp. 

33. Sheffer, H. W., and L. G. Evans. Copper Leaching Practices 
in the Western United States. BuMines IC 8341, 1968, 57 pp. 

34. Skillings Mining Review. 60-50-40 Years Ago. V. 71, No. 19, 
May 8, 1982, p. 18. 

35. Spedden, H. R., E. E. Malouf, and J. D. Davis. In Situ Leaching 
of Copper— Pilot Plant Test. Pres. at Ann. Meeting, AIME New York, 
February 1971, 21 pp; available for consultation at BuMines Twin 
Cities Research Center, Minneapolis, MN. 

36. Steckley, R. C, W. C. Larson, and D. V. D'Andrea. Blasting 
Tests in a Porphyry Copper Deposit in Preparation for In Situ 
Extraction. BuMines Rl 8070, 1975, 47 pp. 

37. Thomas, R. W. Leaching Copper From Worked-Out Areas of 
the Ray Mines, Arizona. Min. and Met., v. 19, November 1938, pp. 
481-485. 

38. Ward, M. H. Surface Blasting Followed by In Situ Leaching 
the Big Mike Mine. Proc. Solution Mining Symp., AIME Ann. Meeting, 
Dallas, TX, Feb. 25-27, 1974, pp. 243-251. 

39. Woodward-Clyde Consultants. Pumping Test Analyses, 
Nacimiento Copper Mine, Cuba, New Mexico. Prepared for Earth 
Resources Co., Cuba, NM, Aug. 1978; available for consultation of 
BuMines Twin Cities Research Center, Minneapolis, MN. 

40. Wormser, F. E. Leaching a Copper Mine. Eng. and Min. J., 
v. 116, No. 16, October 1923, pp. 665-670. 



18 



APPENDIX A.— IN SITU COPPER MINING OPERATING DATA 



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21 



APPENDIX B.— COPPER IN SITU LEACHING BIBLIOGRAPHIES 

1. Anderson, A, E . .. and F. K. Cameron. Recovery of Copper by 
Leaching, Ohio Copper Co. of Utah. Trans. AIME, v. 73, 1926, 
pp. 31-57. 

2. Anderson, M. L. Improved Productivity From In Situ Leaching. 
Proc . on Productivity in Mining, Univ. Missouri — Rolla, Rolla, 
Mo., May 13-15, 1974, ed . by J. J. Scott, pp. 82-83. 

3. Anderson, M. L. < assigned to Mobil Oil Corp., a corp. of New 
York). Methods of Selectively Improving the Fluid 
Communication of Earth Formations. U.S. Pat. 3,565,173, Feb. 
23, 1971. 

4. Antonov, A. A. Forecasting the Effect of Geological Factors 
on Underground Leaching of Copper-Nickel Sulfide Qres . Soviet 
Science J., v. 7, No. 2, February 1971, pp. 179-183. 

5. Arnold, Id. D., and D. J. Crouse. Radioactive Contamination 

of Copper Recovered From Ore Fractured With Nuclear Explosions. 
Oak Ridge National Laboratory, Rept . ORNL-4677, September 1971, 
55 pp . 

6. Austin, U. L. Process of Extracting Copper from Ore. U.S. 
Pat. 975,106, Nov. 8, 1910. 

7. Axen, S., D. Baughman, and R. V. Huff. In Situ Mining - A 
New Engineering Opportunity. SHE Preprint 79-323, 11 pp. 

8. Ballard, J. K. Solution Mining. Min. Eng . , v. 23, No, 2, 
February 1971, p. 109. 

9. Bartlett, R. W. A Combined Pore Diffusion and Chalcopyrite 
Dissolution Kinetics Model for In Situ Leaching of a Fragmented 
Copper Porphyry. Proc. 2d Internat. Symp . on Hydrometal lurgy , 
AIME Ann, Meeting, Chicago, 111., ed . by D. J. I. Evans, and R. 
S. Shoemaker, v. 1, Ch . 14, Feb 25 - Mar. 1, 1973, pp. 331-374. 

10. Bhappu, R. B. Economic Evaluation of In Place Leaching and 
Solution Mining Situations. Pres. at a Short Course in In- 
Place Leaching and Solution Mining, the Mackay School of Mines, 
Univ, Nevada— Reno, Reno, Nev . , Nov. 10-14, 1975, 22 pp.; 
available for consultation at Bureau of Mines Twin Cities 
Research Center, Minneapolis, Minn. 

11. Bhappu, R. B. In Situ Extraction and Leaching Technology. 
Pres, at Inter-Regional Seminar on the Economics of Mineral 
Engineering, Ankara, Turkey, Apr. 5-16, 1976, 39 pp.; 
available for consultation at Bureau of Mines Twin Cities 
Research Center, Minneapolis, Minn, 

12. Bhappu, R, B. In Situ Mining Technology - Practical and 
Economic Aspects, Pres, at the Turkish Mining Institute, 



22 

Ankara, Turkey, Apr. 5-16, 1976, 29 pp.; available for 
consultation at Bureau of Mines Twin Cities Research Center, 
Minneapolis, Minn. 

13. Bhappu, R. B. Past, Present, and Future of Solution Mining. 
Pres. at Fall Meeting and Exhibit, 2nd SME/SPE Internat. Sol. 
Min. Symp . , Soc . Min. Eng . , AIME, Denver, Colo., Nov. 18-20, 
1981 . 

14. Bhappu, R. 6., and F. M. Lewis. Economic Evaluation of 
Available Processes for Treating Oxide Copper Ores. Pres. at 
Fall Meeting, Soc. Min, Eng,, AIME, Acapulco, Mexico, Sept. 22- 
25, 1974, Preprint No. 74-AS-334, 20 pp. 

15. Braithwaite, J. U., and M. E. Wadsworth . Oxidation of 
Chalcopyrite Under Simulated Conditions of Deep Solution 
Mining. Proc. Internat. Symp. on Copper Extraction and 
Refining, Met. Soc, AIME, Las Vegas, Nev . , Feb. 22-26, 1976 
(pub. as Extractive Metallurgy of Copper — Hydrometal lurgy and 
Elect row inning, ed . by J. C. Yannopoulos and J. C. Agarwal). 
Port City Press, Baltimore, Md . , v. II, 1976, pp. 752-775. 

16. Braun, R. L., and A. E. Lewis. Nuclear Solution Mining! Part 
VIII - Oxygen Distribution. Lawrence Radiation Laboratory, 
Rept. UCID-16008, March 1972, 31 pp. 

17. Braun, R. L., A. E. Lewis, and M. E. Wadsworth. In Place 
Leaching of Primary Sulfide Ores: Laboratory Leaching Data 
and Kinetics Model. Proc. Solution Mining Symp,, AIME Ann. 
Meeting, Dallas, Tex., Feb. 25-27, 1974, pp. 295-323.: Met. 
Trans., v. 5, No. 8, August 1974, pp. 1717-1726. 

18. Braun, R. L., and R. G. Mallon. Combined Leach-Circulation 
Calculation for Predicting In-Situ Copper Leaching of Primary 
Sulfide Ore. Trans. Soc. Min. Eng., AIME, v. 258, No. 2, June 

1975, pp, 103-110. 

19. Brier ley, C. L. Column Leaching of Low-Grade Chalcopyrite 
Ore Using Thermophilic Bacteria. (Contract G0177T00, N. Mex. 
Bureau of Mines and Miner. Res. and N. Mex. Inst, of Min. and 
Technol.). BuMines OFR 113-80, July 1979, 96 pp.; HTIS PB 81- 
128498. 

20. Brier ley, C. L. Leaching: Use of a High-Temperature Microbe. 
Ch . 31 in Solution Mining Symposium, ed . by F. F. Alpan, W. 
K. McKinney, and A. D. Pernichele. The American Institute of 
Mining, Metallurgical, and Petroleum Engineers, Inc., New York, 
1974, pp. 461-469. 

21. Br inckerhof f , C. M. Assessment of Research and Development 
Needs and Priorities for In Situ Leaching of Copper. 
(Contract J0166036, C. M. Br inckerhof f. Consultant). July 26, 

1976, 5 pp.; available for consultation at Bureau of Mines 
Twin Cities Research Center, Minneapolis, Minn. 



23 



22. Bruynesteyn, A., and D. U . Duncan. Effect of Particle Size 
on the Microbiological Leaching of Chalcopyrite Bearing Ore. 
Proc. Solution Mining Symp., AIME Ann. Meeting, Dallas, Texas, 
Feb. 25-27, t974, pp. 324-337. 

23. Cannon, K. J. Solvent Extraction - Electrowinning Technology 
for Copper. Australian Mining, v. 69, No. 3, March 1977, pp. 
47-51 . 

24. Carnahan, T. G., and H, J. Heinen (assigned to U.S. Department 
of the Interior). Chemical Mining of Copper Porphyry Ores. 
U.S. Pat. 3,912,330, Oct. 14, 1975. 

25. Carnahan, T. G., and H. J. Heinen. Simulated In Situ Leaching 
of Copper from a Porphyry Ore. BuMines TPR 69, May 1973, 11 

PP- 

26. Carpenter, R. H., and R. B. Bhappu . Hydrometal lurgy and Low 
Gr3de Ore Potential. PreiS . at 106th Ann. Meeting, AIME, 
Atlanta, Ga . , Mar. 6-10, 1977. 

27. Catanach, C. B. Development and In Place Leaching of Mountain 
City Chalcocite Ore Body. Proc. Internat. Symp . on Copper 
Extraction and Refining, Met. Soc . , AIME, Las Vegas, Nev . , 
Feb . 22-; 
Hydrome 
and J 
1976, pp , 849-872. 



>alcocite ure Body. Proc. Internat. Symp. on topper 
^ion and Refining, Met. Soc., AIME, Las Vegas, Hev., 
i— 26 , 1976 (pub. as Extractive Metallurgy of Copper — 
>tallurgy and Electrowinning, ed . by J. C. Yannopoulos 
C. Agarwal). Port City Press, Baltimore, Md . , v. II, 
>D . 849-872. 



28. Catanach, C. B., E. F. Moran, D. D. Porter, C. G. Rudershausen, 
and R, U. Sommers , Copper Leaching from an Orebody Blasted 

In Place. In Situ, v. 1, Ho. 4, 1977, pp. 283-303. 

29. Chamberlain, C, J. Newton, and D. Clifton. How Cyanidation 
Can Treat Copper Ores. Eng . and Min. J., v. 170, No. 10, 
October 1969, pp. 90-91. 

30. Chamber lain, P. G. In-Place Leaching Research at the Seneca 
Mine, Mohawk, Mich. Pres. at Ann. Spring Technical Meeting 

of Upper Peninsula Section, AIME, Michigan Technological Univ., 
Houghton, Mich., Apr. 21, 1977, 14 pp.; available for 
consultation at Bureau of Mines Twin Cities Research Center, 
Minneapolis, Minn. 

31. Chase, C. K,, E. A. Nordhousen, R. B. Bhappu, J. B. Fletcher, 
J. V. Rouse, and U . D. Gould. Feasibility of In Situ Leaching 
of Depleted Underground Copper and Uranium Mines. (Contract 
J0295045, Mountain States Research and Development, Inc.). 
January 1982, in two volumes, v. 1, 115 pp., v. 2, 81 pp. 

32. Chilson, R, E. Continuously Leaching an Ore Column. U.S. 
Pat. 4,071,611, Jan. 31, 1978. 

33. Cooper, F. D. Copper Hydrometal lurgy ; A Review and Outlook. 
BuMines IC 8394, 1968, 18 pp. 



24 

34. Coursen, D, L. < assigned to E . I. du Pont de Nemours & Co . , 
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44. Davidson, D. H. In-Situ Leaching of Nonferrous Metals. Min. 
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47. Davidson, D. H., R. V. Huff, and W. E. Sonstelie. Measurement 
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51 . 



52 



54 



55 



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26 

Resource Tech. Seminar II. Colorado School of Mines, Golden, 
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56. Engineering and Mining Journal. AEC and KCC Will Jointly 
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57. Engineering and Mining Journal. Asarco and Dow Chemical to 
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58. Engineering and Mining Journal . Copper Leaching with Cyanide 
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59. Engineering and Mining Journal. Economics Provide Motive for 
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60. Engineering and Mining Journal. The Estimated Cost of a 
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61. Engineering and Mining Journal. India Studies Possibility of 
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64. Engineering and Mining Journal. The Oxymin Project at Miami, 
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65. Engineering and Mining Journal. Ranchers Big Blast Shatters 
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66. Engineering and Mining Journal. Solution Mining Opening New 
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68. Finlay, U. L. Molecular Mining of Keweenaw Copper, A Prime 
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69. Fitch, J, L., and B. G. Hurd (assigned to Mobil Oil Corp., 
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72. Fletcher, J. B. In Place Leaching at Miami Mine, Miami, 
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80. Groves, R. D., T. H. J^ff^rs t and G. M. Potter. Leaching 
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28 

82. Hansen, S, M,, and A. R. Jager . How To Make Ore From Marginal 
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83. Hard, R. A. < assigned to Kennecott Copper Corp., Hew York). 
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84. Hardwick, W. R. Fracturing a Deposit With Huclear Explosives 
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87. Hockings, W. A., and W. L. Freyberger. A Plan for Determining 
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88. Hogan, D, K. In-Situ Copper Leaching at the Old Reliable Mine. 
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89. Holderreed, F. L. Copper Extraction by the Acid Leaching of 
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90. Hougen, L, R., and H, Zachariasen. Recovery of Hickel, Copper 
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94. Huff, R. V., and H. Davidson. In-Situ Leaching Materials 
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29 

Exhibition, Soc . Petrol. Eng . , AIHE, Las Vegas, Nev . , Sept. 
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95. Huff, R. V., and P. A. Huska (assigned to Kennecott Copper 
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96. Huff, R. V., and D. J. Moynihan (assigned to kennecott Copper 
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97. Hunkin, G. G. A Review of In Situ Leaching. Pres. at AIME 
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98. Hurd, B. G., and J. L. Fitch (assigned to Mobil 8x1 Corp., 
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102. Johnson, P. H., and R. B. Bhappu . Chemical Mining - A Study 
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103. Johnson, P. H., and R. 8. Bhappu. Chemical Mining - 
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104. kaczynski, D. A., G. W. Lower, and U. A. Hockings. Kinetics 
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105. Kalabin, A. I. Winning of Useful Elements from Minerals by 
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106. Kelseaux, R. M. (assigned to Cities Service Oil Co.., Tulsa, 
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30 



107. Keyes, H. E. Discussion of In Place Leaching at Miami Mine, 
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108. Lampard, W. J. < assigned to Kennecott Copper Corp., New York). 
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109. Larson, D. R. A Report Comparing Open Pit Mining and Heap 
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111. Laswell, G. W. Wanted: Rotary Drilling Technology for In Situ 
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112. Leach, D. L., and R. L. Braun. Leaching of Primary Sulfide 
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113. Lewis, A. E. Chemical Mining of Primary Copper Ores by Use 

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116. Lewis, A. E., and R. L. Braun. Nuclear Chemical Mining of 
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117. Lewis, A. E., R. L. Braun, C. J. Sisemore, and R. G. Mai Ion. 
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120. Longwell, R. L. In Place Leaching of a Mixed Copper Ore Body. 
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121. Malouf, E. E. Copper Leaching Practices. Pres . at Ann. 
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122. Malouf, E, E. Introduction to Dump Leaching Practice. Part 
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123. Malouf, E. E. Leaching as a Mining Tool. Internat . Symp. on 
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124. Malouf, E. E. The Role of Microorganisms in Chemical Mining. 
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125. Mayling, A. A. Method for Extracting Copper, Zinc, Lead, 
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127. Michigan Technological University. A Plan for Determining 
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128. Miller, J, D. Processing of Leach Liquors Produced by Nuclear 
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t33. Mining Engineering. Ranchers Development Sets Off Blast, Will 
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134. Mining Magazine, In Situ Copper Leaching at the Old Reliable 
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136. Mining Record (Denver', Colo.). Ranchers Blasts Old Reliable 
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137. Murphy, J, New Returns From Old Reliable. 4 pp.; available 
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139. Myers, D. L. Mining Copper In Situ. The Mines Mag... v. 31, 
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146. Pings> w" . B. Bacterial Leaching. Miner. Ind. Bull., v. 2, 
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148. Porter, D. D. Blast Design for In Situ Leaching. Pres . at 
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151. Prescott Newspaper (Prescott, Ariz.). Kirkland Blast Will 
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152. Rabb, D. D. Leaching of Copper Ores and the Use of Bacteria. 
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154. Rabb, D. D. Solution Mining. Min. Eng., v. 24, No. 2, 
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155. Raghavan, S. Ammoniacal Leaching of a Chrysocolla Bearing 
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34 

159. Roman, R. J. The Limitations of Laboratory Testing and 
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166. St. Peter, A. L. In Situ Leaching of Orebodies Design and 
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35 

14th Internat. Symp . on the Application of Computer Methods 

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36 

186. Stauter, J. C, and A, G. Fonseca . Leaching of Oxide Copper 
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37 



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